Switch host builds to use Clang by default.

If LOCAL_CLANG is not set to false for a host module, clang will be used instead of gcc.

This also enables the integrated assembler by default for Darwin host builds.

bug 16172793

Change-Id: If7484c5dbcccce7d925bec97bff0a3e4c30e9434
diff --git a/core/clang/config.mk b/core/clang/config.mk
index f50a0cb..59cb38e 100644
--- a/core/clang/config.mk
+++ b/core/clang/config.mk
@@ -41,7 +41,8 @@
   -Wmaybe-uninitialized \
   -Wno-maybe-uninitialized \
   -Wno-error=maybe-uninitialized \
-  -fno-canonical-system-headers
+  -fno-canonical-system-headers \
+  -Wno-unused-local-typedefs
 
 # Clang flags for all host rules
 CLANG_CONFIG_HOST_EXTRA_ASFLAGS :=