Add more support for GLOBAL_CONLYFLAGS.

This will be necessary to support -std=gnu99 mode for clang 3.6, which
defaults to C11 mode (unlike prior releases that use C99).

Change-Id: Iea84582f9f12ba76b988463cbc0a20bd61042538
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 8ee7734..9f339ff 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -48,6 +48,7 @@
 LOCAL_CPPFLAGS:=
 LOCAL_CLANG_ASFLAGS:=
 LOCAL_CLANG_CFLAGS:=
+LOCAL_CLANG_CONLYFLAGS:=
 LOCAL_CLANG_CPPFLAGS:=
 LOCAL_CONLYFLAGS:=
 LOCAL_RTTI_FLAG:=