Set USE_CLANG_PLATFORM_BUILD to default true.

BUG: 26102335
Change-Id: I3b9fa2dfbee361410caf163147945ab448bb8ddf
diff --git a/core/envsetup.mk b/core/envsetup.mk
index 050d445..6c38e99 100644
--- a/core/envsetup.mk
+++ b/core/envsetup.mk
@@ -426,3 +426,7 @@
 ifeq ($(PRINT_BUILD_CONFIG),)
 PRINT_BUILD_CONFIG := true
 endif
+
+ifeq ($(USE_CLANG_PLATFORM_BUILD),)
+USE_CLANG_PLATFORM_BUILD := true
+endif