Allow UniversalArchs variable to be overridden on a per-config basis.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@93816 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/Makefile b/Makefile
index 79149e3..95c02a6 100644
--- a/Makefile
+++ b/Makefile
@@ -136,7 +136,9 @@
 # not.
 $(call Set,Tmp.ArchsToBuild,\
   $(if $(call IsDefined,$(Tmp.Key).UniversalArchs),\
-       $($(Tmp.Key).UniversalArchs),\
+       $(strip \
+         $(or $($(Tmp.Key).UniversalArchs.$(Tmp.Config)),\
+              $($(Tmp.Key).UniversalArchs))),\
        $(call VarOrDefault,$(Tmp.Key).Arch.$(Tmp.Config),$($(Tmp.Key).Arch))))
 
 # Copy or lipo to create the per-config library.