gnu: freecad: Fix build.

* gnu/packages/patches/freecad-boost-serialization.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/engineering.scm (freecad) [source]: Use it.
[arguments]{#:configure-flags}: Turn it into a GEXP and adapt it.

gnu/local.mk

@@ -1056,6 +1056,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/fp16-system-libraries.patch		\
   %D%/packages/patches/fpc-reproducibility.patch		\
   %D%/packages/patches/fplll-std-fenv.patch     		\
+  %D%/packages/patches/freecad-boost-serialization.patch	\
   %D%/packages/patches/freecad-vtk9.patch			\
   %D%/packages/patches/freedink-engine-fix-sdl-hints.patch	\
   %D%/packages/patches/freedink-engine-fix-sdl-hints.patch	\

gnu/packages/engineering.scm

@@ -2381,7 +2381,8 @@ comments.")))
        (file-name (git-file-name name version))
        (sha256
         (base32 "0fhjv0x3dix1c7jml91yx63z9xifjlbhjbcdb73lw80smpxrq7mm"))
-       (patches (search-patches "freecad-vtk9.patch"))))
+       (patches (search-patches "freecad-vtk9.patch"
+                                "freecad-boost-serialization.patch"))))
     (build-system qt-build-system)
     (native-inputs
      `(("doxygen" ,doxygen)
@@ -2434,28 +2435,31 @@ comments.")))
     (arguments
      `(#:tests? #f          ; Project has no tests
        #:configure-flags
-       (list
-        "-DBUILD_QT5=ON"
-        "-DBUILD_FLAT_MESH:BOOL=ON"
-        (string-append "-DCMAKE_INSTALL_LIBDIR=" (assoc-ref %outputs "out") "/lib")
-        (string-append "-DPYSIDE2UICBINARY="
-                       (assoc-ref %build-inputs "python-pyside-2-tools")
-                       "/bin/uic")
-        (string-append "-DPYSIDE2RCCBINARY="
-                       (assoc-ref %build-inputs "python-pyside-2-tools")
-                       "/bin/rcc")
-        "-DPYSIDE_LIBRARY=PySide2::pyside2"
-        (string-append
-         "-DPYSIDE_INCLUDE_DIR="
-         (assoc-ref %build-inputs "python-pyside-2") "/include;"
-         (assoc-ref %build-inputs "python-pyside-2") "/include/PySide2;"
-         (assoc-ref %build-inputs "python-pyside-2") "/include/PySide2/QtCore;"
-         (assoc-ref %build-inputs "python-pyside-2") "/include/PySide2/QtWidgets;"
-         (assoc-ref %build-inputs "python-pyside-2") "/include/PySide2/QtGui;")
-        "-DSHIBOKEN_LIBRARY=Shiboken2::libshiboken"
-        (string-append "-DSHIBOKEN_INCLUDE_DIR="
-                       (assoc-ref %build-inputs "python-shiboken-2")
-                       "/include/shiboken2"))
+       ,#~(list
+           "-DBUILD_QT5=ON"
+           "-DBUILD_FLAT_MESH:BOOL=ON"
+           "-DBUILD_ENABLE_CXX_STD:STRING=C++17"
+           (string-append "-DCMAKE_INSTALL_LIBDIR=" #$output "/lib")
+           (string-append "-DPYSIDE2UICBINARY="
+                          #$(this-package-native-input
+                             "python-pyside-2-tools")
+                          "/bin/uic")
+           (string-append "-DPYSIDE2RCCBINARY="
+                          #$(this-package-native-input
+                             "python-pyside-2-tools")
+                          "/bin/rcc")
+           "-DPYSIDE_LIBRARY=PySide2::pyside2"
+           (string-append
+            "-DPYSIDE_INCLUDE_DIR="
+            #$(this-package-input "python-pyside-2") "/include;"
+            #$(this-package-input "python-pyside-2") "/include/PySide2;"
+            #$(this-package-input "python-pyside-2") "/include/PySide2/QtCore;"
+            #$(this-package-input "python-pyside-2") "/include/PySide2/QtWidgets;"
+            #$(this-package-input "python-pyside-2") "/include/PySide2/QtGui;")
+           "-DSHIBOKEN_LIBRARY=Shiboken2::libshiboken"
+           (string-append "-DSHIBOKEN_INCLUDE_DIR="
+                          #$(this-package-input "python-shiboken-2")
+                          "/include/shiboken2"))
        #:phases
        (modify-phases %standard-phases
          (add-before 'configure 'restore-pythonpath

gnu/packages/patches/freecad-boost-serialization.patch

@@ -0,0 +1,27 @@
+Taken from: https://github.com/archlinux/svntogit-community/blob/packages/freecad/trunk/freecad-boost.patch.
+
+Index: FreeCAD-0.19.2/CMakeLists.txt
+===================================================================
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -46,6 +46,7 @@ if(NOT FREECAD_LIBPACK_USE OR FREECAD_LI
+     SetupPCL()
+     SetupPybind11()
+     SetupBoost()
++	set(Boost_LIBRARIES_App ${Boost_LIBRARIES})
+     SetupXercesC()
+     find_package(ZLIB REQUIRED)
+     find_package(PyCXX REQUIRED)
+Index: FreeCAD-0.19.2/src/App/CMakeLists.txt
+===================================================================
+--- a/src/App/CMakeLists.txt
++++ b/src/App/CMakeLists.txt
+@@ -59,7 +59,7 @@ include_directories(
+ 
+ set(FreeCADApp_LIBS
+     FreeCADBase
+-    ${Boost_LIBRARIES}
++    ${Boost_LIBRARIES_App}
+ )
+ 
+ if (BUILD_QT5)