Bug 40606: Use Clang to compile NSIS

NSIS officially supports only MSVC and GCC as compilers, so it was one
of the two projects forcing us to keep a GCC toolchain for Windows.
With this commit, we adapt the tricks Mozilla uses to build NSIS with
Clang, and remove the dependency on mingw-w64.

The main trick is to use the GNU assembler instead of Clang's internal
one to build NSIS's system plugin. Luckily, it can be found in
binutils, without a full GCC build.

projects/nsis/build

@@ -4,10 +4,38 @@
 mkdir -p /var/tmp/build
 tar -C /var/tmp/build -xf nsis-[% c('version') %].tar.bz2
 
+# We need the GNU assembler for the system plugin
+tar -C /var/tmp/dist -xf [% c('input_files_by_name/binutils') %]
+
 # NSIS requires zlib and we later set the path using ZLIB_W32.
 tar -C /var/tmp/build -xf [% c('input_files_by_name/zlib') %]
 
+# This trick is adapted from Firefox's
+# taskcluster/scripts/misc/build-mingw32-nsis.sh
+compiler_prefix=/var/tmp/dist/mingw-w64-clang/bin/[% c("arch") %]-w64-mingw32
+cat <<'EOF' >"$compiler_prefix-gcc"
+#!/bin/sh
+# SCons ignores the external $PATH, so we add binutils here.
+export PATH=/var/tmp/dist/binutils/bin:$PATH
+case "$@" in
+*/Call*.S)
+  $(dirname $0)/[% c("arch") %]-w64-mingw32-clang -fno-integrated-as "$@"
+  ;;
+*)
+  $(dirname $0)/[% c("arch") %]-w64-mingw32-clang "$@"
+  ;;
+esac
+EOF
+
+chmod +x "$compiler_prefix-gcc"
+ln -s "$compiler_prefix-clang++" "$compiler_prefix-g++"
+
 cd /var/tmp/build/nsis-[% c('version') %]-src
+
+# These two sed commands also come from build-mingw32-nsis.sh
+sed -i 's/-Wl,--exclude-libs,msvcrt.a/-Wl,-Xlink=-fixed/' SCons/Config/gnu
+sed -i '2i extern "C"' SCons/Config/{memcpy,memset}.c
+
 # Adding --no-insert-timestamp to APPEND_LINKFLAGS is not working as it
 # is used for both the host and cross-compiled parts, but this option is
 # only valid for the Windows linker. Therefore we add it using a patch
@@ -30,8 +58,7 @@ patch -p1 < $rootdir/no-reloc-section.diff
 [% END %]
 
 [% SET scons_args = 'VERSION=' _ c("version")
-        _ ' APPEND_CCFLAGS="-fgnu89-inline"'
-        _ " SKIPUTILS='NSIS Menu' XGCC_W32_PREFIX=" _ c("arch") _ "-w64-mingw32-"
+        _ " SKIPUTILS='NSIS Menu,Makensisw' XGCC_W32_PREFIX=" _ c("arch") _ "-w64-mingw32-"
         _ " TARGET_ARCH=" _ target
         _ " ZLIB_W32=/var/tmp/build/zlib/"
         _ ' PREFIX=/var/tmp/dist/nsis' -%]

projects/nsis/config

@@ -11,12 +11,6 @@ var:
     - zlib1g-dev
     - libcppunit-dev
     - xsltproc
-  # NSIS has an assembly part that cannot be compiled with Clang.
-  # Mozilla uses -fno-integrated-as (see
-  # taskcluster/scripts/misc/build-mingw32-nsis.sh) but for some reason this
-  # does not seem to work for us, so just keep GCC for the moment, since we are
-  # already using it for Rust anyway.
-  compiler: mingw-w64
 
 input_files:
   - project: container-image
@@ -27,5 +21,7 @@ input_files:
   - filename: no-reloc-section.diff
   - name: '[% c("var/compiler") %]'
     project: '[% c("var/compiler") %]'
+  - name: binutils
+    project: binutils
   - name: zlib
     project: zlib