Bug 1188766 - Avoid exporting UPLOAD_EXTRA_FILES from mozconfig. r=mshal

The way UPLOAD_EXTRA_FILES is currently exported makes the files added
to the list added in each directory that is being traversed recursively
because of the += in .mozconfig.mk, combined with "export".

The easy way out is to remove the export altogether, but being unsure of
the side effects of putting all non exported mk_add_options variables
in .mozconfig.mk, limit this to UPLOAD_EXTRA_FILES.

build/mozconfig.cache

@@ -60,7 +60,7 @@ else
     ac_add_options "--with-compiler-wrapper=python2.7 $topsrcdir/sccache/sccache.py"
     mk_add_options MOZ_PREFLIGHT_ALL+=build/sccache.mk
     mk_add_options MOZ_POSTFLIGHT_ALL+=build/sccache.mk
-    mk_add_options "export UPLOAD_EXTRA_FILES+=sccache.log.gz"
+    mk_add_options "UPLOAD_EXTRA_FILES+=sccache.log.gz"
     case "$platform" in
     win*)
         # sccache supports a special flag to create depfiles.

client.mk

@@ -190,9 +190,10 @@ WANT_MOZCONFIG_MK = 1
 endif
 
 ifdef WANT_MOZCONFIG_MK
-# For now, only output "export" lines from mach environment --format=client.mk output.
-MOZCONFIG_MK_LINES := $(filter export||%,$(MOZCONFIG_OUT_LINES))
-$(OBJDIR)/.mozconfig.mk: $(FOUND_MOZCONFIG) $(call mkdir_deps,$(OBJDIR)) $(OBJDIR)/CLOBBER
+# For now, only output "export" lines and lines containing UPLOAD_EXTRA_FILES
+# from mach environment --format=client.mk output.
+MOZCONFIG_MK_LINES := $(filter export||% UPLOAD_EXTRA_FILES% %UPLOAD_EXTRA_FILES%,$(MOZCONFIG_OUT_LINES))
+$(OBJDIR)/.mozconfig.mk: client.mk $(FOUND_MOZCONFIG) $(call mkdir_deps,$(OBJDIR)) $(OBJDIR)/CLOBBER
 	$(if $(MOZCONFIG_MK_LINES),( $(foreach line,$(MOZCONFIG_MK_LINES), echo '$(subst ||, ,$(line))';) )) > $@
 
 # Include that makefile so that it is created. This should not actually change
@@ -201,12 +202,6 @@ $(OBJDIR)/.mozconfig.mk: $(FOUND_MOZCONFIG) $(call mkdir_deps,$(OBJDIR)) $(OBJDI
 include $(OBJDIR)/.mozconfig.mk
 endif
 
-# UPLOAD_EXTRA_FILES is appended to and exported from mozconfig, which makes
-# submakes as well as configure add even more to that, so just unexport it
-# for submakes to pick it from .mozconfig.mk and for configure to pick it
-# from mach environment.
-unexport UPLOAD_EXTRA_FILES
-
 # Print out any options loaded from mozconfig.
 all realbuild clean distclean export libs install realclean::
 ifneq (,$(strip $(MOZCONFIG_OUT_FILTERED)))