gnu: mrustc: Update to 0.8.1.

* gnu/packages/patches/mrustc-0.8.0-fix-variable-length-integer-receiving.patch: Delete file.
* gnu/local.mk (dist_patch_DATA): Remove it.
* gnu/packages/rust.scm (mrustc): Update to 0.8.1.
[source](patches): Remove it.
[native-inputs]: Add zlib.

gnu/local.mk

@@ -1180,7 +1180,6 @@ dist_patch_DATA =						\
   %D%/packages/patches/mozjs38-tracelogger.patch		\
   %D%/packages/patches/mozjs38-version-detection.patch		\
   %D%/packages/patches/mrrescue-support-love-11.patch		\
-  %D%/packages/patches/mrustc-0.8.0-fix-variable-length-integer-receiving.patch \
   %D%/packages/patches/mtools-mformat-uninitialized.patch	\
   %D%/packages/patches/mumps-build-parallelism.patch		\
   %D%/packages/patches/mumps-shared-libseq.patch		\

gnu/packages/patches/mrustc-0.8.0-fix-variable-length-integer-receiving.patch

@@ -1,15 +0,0 @@
-https://github.com/thepowersgang/mrustc/issues/109
-From: Danny Milosavljevic <dannym@scratchpost.org>
-Date: Fri, 3 Jan 2019 13:00:00 +0100
-
---- mrustc/src/expand/proc_macro.cpp.orig	2019-02-01 14:16:54.208486062 +0100
-+++ mrustc/src/expand/proc_macro.cpp	2019-02-01 14:17:14.350925705 +0100
-@@ -977,7 +977,7 @@
-     for(;;)
-     {
-         auto b = recv_u8();
--        v |= static_cast<uint64_t>(b) << ofs;
-+        v |= static_cast<uint64_t>(b & 0x7F) << ofs;
-         if( (b & 0x80) == 0 )
-             break;
-         ofs += 7;

gnu/packages/rust.scm

@@ -91,7 +91,7 @@
   (let ((rustc-version "1.19.0"))
     (package
       (name "mrustc")
-      (version "0.8.0")
+      (version "0.8.1")
       (source (origin
                 (method git-fetch)
                 (uri (git-reference
@@ -100,9 +100,7 @@
                 (file-name (git-file-name name version))
                 (sha256
                  (base32
-                  "0a7v8ccyzp1sdkwni8h1698hxpfz2sxhcpx42n6l2pbm0rbjp08i"))
-                (patches
-                 (search-patches "mrustc-0.8.0-fix-variable-length-integer-receiving.patch"))))
+                  "00800zckq009kf9v3hb8kp1svryvq3jpg4439ksm3wcidjvszdzc"))))
       (outputs '("out" "cargo"))
       (build-system gnu-build-system)
       (inputs
@@ -111,7 +109,8 @@
        `(("bison" ,bison)
          ("flex" ,flex)
          ;; Required for the libstd sources.
-         ("rustc" ,(package-source rust-1.19))))
+         ("rustc" ,(package-source rust-1.19))
+         ("zlib" ,zlib)))
       (arguments
        `(#:test-target "local_tests"
          #:make-flags (list (string-append "LLVM_CONFIG="