Bug 1657863 - Skip adding manifests automatically on mingw builds. r=froydnj

This wasn't happening before bug 1656141 and apparently causes problems.
So until we can sort them out...

Differential Revision: https://phabricator.services.mozilla.com/D86638

config/rules.mk

@@ -404,7 +404,12 @@ ifeq ($(MOZ_WIDGET_TOOLKIT),windows)
 resfile = $(notdir $1).res
 # We also build .res files for simple programs if a corresponding manifest
 # exists. We'll generate a .rc file that includes the manifest.
+ifdef GNU_CC
+# Skip on mingw builds because of bug 1657863
+resfile_for_manifest =
+else
 resfile_for_manifest = $(if $(wildcard $(srcdir)/$(notdir $1).manifest),$(call resfile,$1))
+endif
 else
 resfile =
 resfile_for_manifest =