gnu: Use GCC 7 as the default compiler.

* gnu/packages/cross-base.scm (%gcc-cross-include-paths): Remove
CROSS_C_INCLUDE_PATH & co in favor of CROSS_CPATH.
* gnu/build/cross-toolchain.scm (%gcc-cross-include-paths): Likewise.
(cross-gcc-build-phases): Set CROSS_C_INCLUDE_PATH and
CROSS_CPLUS_INCLUDE_PATH when building the cross GCC.
* gnu/packages/commencement.scm (libstdc++): Add
"--disable-libstdcxx-dual-abi" to #:configure-flags.
(gcc-boot0)[arguments]: Add "--disable-libmpx"
to #:configure-flags.
(gcc-final): Add phase to set C_INCLUDE_PATH and CPLUS_INCLUDE_PATH before
building GCC.
(gcc-toolchain-5): Use MAKE-GCC-TOOLCHAIN.
(gcc-toolchain-7): Change to GCC-TOOLCHAIN.
* gnu/packages/gcc.scm (gcc): Change from GCC-5 to GCC-7.
(gfortran): Change to GFORTRAN-7.
(gcc-objc): Change to GCC-OBJC-7.
(gcc-objc++): Change to GCC-OBJC++-7.
* gnu/packages/rust.scm (rust-1.19.0)[native-search-paths]: Change from
C_INCLUDE_PATH & co to CPATH.

gnu/build/cross-toolchain.scm

@@ -3,6 +3,7 @@
 ;;; Copyright © 2014, 2015, 2018 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2016 Jan Nieuwenhuizen <janneke@gnu.org>
 ;;; Copyright © 2016 Manolis Fragkiskos Ragkousis <manolis837@gmail.com>
+;;; Copyright © 2019 Marius Bakke <mbakke@fastmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -36,11 +37,8 @@
 
 (define %gcc-include-paths
   ;; Environment variables for header search paths.
-  ;; Note: See <http://bugs.gnu.org/22186> for why not 'CPATH'.
+  ;; Note: See <http://bugs.gnu.org/30756> for why not 'C_INCLUDE_PATH' & co.
-  '("C_INCLUDE_PATH"
+  '("CPATH"))
-    "CPLUS_INCLUDE_PATH"
-    "OBJC_INCLUDE_PATH"
-    "OBJCPLUS_INCLUDE_PATH"))
 
 (define %gcc-cross-include-paths
   ;; Search path for target headers when cross-compiling.
@@ -171,6 +169,16 @@ a target triplet."
       (if (string-contains target "mingw")
           set-cross-path/mingw
           set-cross-path))
+    (add-before 'configure 'treat-glibc-as-system-header
+      (lambda* (#:key inputs #:allow-other-keys)
+        (let ((libc (assoc-ref inputs "libc")))
+          (when libc
+            ;; For GCC6 and later, make sure Glibc is treated as a "system
+            ;; header" such that #include_next does the right thing.
+            (for-each (lambda (var)
+                        (setenv var (string-append libc "/include")))
+                      '("CROSS_C_INCLUDE_PATH" "CROSS_CPLUS_INCLUDE_PATH")))
+          #t)))
     (add-after 'install 'make-cross-binutils-visible
       (cut make-cross-binutils-visible #:target target <...>))
     (replace 'install install-strip)))

gnu/packages/commencement.scm

@@ -6,6 +6,7 @@
 ;;; Copyright © 2017, 2018, 2019 Efraim Flashner <efraim@flashner.co.il>
 ;;; Copyright © 2018 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;; Copyright © 2018 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+;;; Copyright © 2019 Marius Bakke <mbakke@fastmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -1578,6 +1579,7 @@ exec " gcc "/bin/" program
                             "--disable-libsanitizer"
                             "--disable-libitm"
                             "--disable-libgomp"
+                            "--disable-libmpx"
                             "--disable-libcilkrts"
                             "--disable-libvtv"
                             "--disable-libssp"
@@ -2118,6 +2120,7 @@ exec ~a/bin/~a-~a -B~a/lib -Wl,-dynamic-linker -Wl,~a/~a \"$@\"~%"
          ;; except for the configure-flags.
          ,@(package-arguments lib)
          #:configure-flags `("--disable-shared"
+                             "--disable-libstdcxx-dual-abi"
                              "--disable-libstdcxx-threads"
                              "--disable-libstdcxx-pch"
                              ,(string-append "--with-gxx-include-dir="
@@ -2207,6 +2210,15 @@ exec ~a/bin/~a-~a -B~a/lib -Wl,-dynamic-linker -Wl,~a/~a \"$@\"~%"
                                            char-set:letter)
                                          ,(package-name lib)))
                              (list gmp-6.0 mpfr mpc))
+                      #t)))
+                (add-before 'configure 'treat-glibc-as-system-header
+                  (lambda* (#:key inputs #:allow-other-keys)
+                    (let ((libc (assoc-ref inputs "libc")))
+                      ;; Make sure Glibc is treated as a "system header" so
+                      ;; #include_next does the right thing.
+                      (for-each (lambda (var)
+                                  (setenv var (string-append libc "/include")))
+                                '("C_INCLUDE_PATH" "CPLUS_INCLUDE_PATH"))
                       #t))))))))
 
     ;; This time we want Texinfo, so we get the manual.  Add
@@ -2455,23 +2467,23 @@ and binaries, plus debugging symbols in the 'debug' output), and Binutils.")
               ("libc-debug" ,glibc-final "debug")
               ("libc-static" ,glibc-final "static")))))
 
+(define-public gcc-toolchain
+  (make-gcc-toolchain gcc-final))
+
 (define-public gcc-toolchain-4.8
   (make-gcc-toolchain gcc-4.8))
 
 (define-public gcc-toolchain-4.9
   (make-gcc-toolchain gcc-4.9))
 
-(define-public gcc-toolchain
-  (make-gcc-toolchain gcc-final))
-
 (define-public gcc-toolchain-5
-  gcc-toolchain)
+  (make-gcc-toolchain gcc-5))
 
 (define-public gcc-toolchain-6
   (make-gcc-toolchain gcc-6))
 
 (define-public gcc-toolchain-7
-  (make-gcc-toolchain gcc-7))
+  gcc-toolchain)
 
 (define-public gcc-toolchain-8
   (make-gcc-toolchain gcc-8))

gnu/packages/cross-base.scm

@@ -51,11 +51,8 @@
 
 (define %gcc-include-paths
   ;; Environment variables for header search paths.
-  ;; Note: See <http://bugs.gnu.org/22186> for why not 'CPATH'.
+  ;; Note: See <http://bugs.gnu.org/30756> for why not 'C_INCLUDE_PATH' & co.
-  '("C_INCLUDE_PATH"
+  '("CPATH"))
-    "CPLUS_INCLUDE_PATH"
-    "OBJC_INCLUDE_PATH"
-    "OBJCPLUS_INCLUDE_PATH"))
 
 (define %gcc-cross-include-paths
   ;; Search path for target headers when cross-compiling.

gnu/packages/gcc.scm

@@ -522,7 +522,7 @@ It also includes runtime support libraries for these languages.")))
 ;; Note: When changing the default gcc version, update
 ;;       the gcc-toolchain-* definitions and the gfortran definition
 ;;       accordingly.
-(define-public gcc gcc-5)
+(define-public gcc gcc-7)
 
 (define-public (make-libstdc++ gcc)
   "Return a libstdc++ package based on GCC.  The primary use case is when
@@ -660,7 +660,7 @@ as the 'native-search-paths' field."
   ;; (custom-gcc gcc "fortran" …) because that would lead to a package object
   ;; that is not 'eq?' with GFORTRAN-5, and thus 'fold-packages' would
   ;; report two gfortran@5 that are in fact identical.
-  gfortran-5)
+  gfortran-7)
 
 (define-public gccgo-4.9
   (custom-gcc gcc-4.9 "gccgo" '("go")
@@ -724,7 +724,7 @@ as the 'native-search-paths' field."
                      (variable "LIBRARY_PATH")
                      (files '("lib" "lib64"))))))
 
-(define-public gcc-objc gcc-objc-5)
+(define-public gcc-objc gcc-objc-7)
 
 (define-public gcc-objc++-4.8
   (custom-gcc gcc-4.8 "gcc-objc++" '("obj-c++")
@@ -780,7 +780,7 @@ as the 'native-search-paths' field."
                      (variable "LIBRARY_PATH")
                      (files '("lib" "lib64"))))))
 
-(define-public gcc-objc++ gcc-objc++-5)
+(define-public gcc-objc++ gcc-objc++-7)
 
 (define (make-libstdc++-doc gcc)
   "Return a package with the libstdc++ documentation for GCC."

gnu/packages/rust.scm

@@ -406,10 +406,7 @@ test = { path = \"../libtest\" }
     ;; modules (see <https://bugs.gnu.org/31392>).
     (native-search-paths
      (list (search-path-specification
-            (variable "C_INCLUDE_PATH")
+            (variable "CPATH")
-            (files '("include")))
-           (search-path-specification
-            (variable "CPLUS_INCLUDE_PATH")
             (files '("include")))
            (search-path-specification
             (variable "LIBRARY_PATH")