Bug 1490566 Do not pass --enable-stdcall-fixup to clang in a x86 Windows build r=froydnj

clang doesn't recognize --enable-stdcall-fixup as an option. We needed this for the
mingw-gcc build (added in Bug 787653) because gcc had difficulty dealing with
Angle's symbol linking

Differential Revision: https://phabricator.services.mozilla.com/D6072

--HG--
extra : moz-landing-system : lando

old-configure.in

@@ -1068,7 +1068,10 @@ case "$target" in
         if test -n "$GNU_CC"; then
             CFLAGS="$CFLAGS -mstackrealign"
             CXXFLAGS="$CXXFLAGS -mstackrealign"
-            LDFLAGS="$LDFLAGS -Wl,--enable-stdcall-fixup -Wl,--large-address-aware"
+            LDFLAGS="$LDFLAGS -Wl,--large-address-aware"
+            if test -z "$CLANG_CC"; then
+                LDFLAGS="$LDFLAGS -Wl,--enable-stdcall-fixup"
+            fi
         else
             DSO_LDOPTS="$DSO_LDOPTS -MACHINE:X86"
             LDFLAGS="$LDFLAGS -SAFESEH"