Move x86_64 target to clang by default.

Bug: 23163853
Change-Id: I0587ec75c0000ac99562233de33147ec8e120e65
diff --git a/target/board/generic_x86_64/BoardConfig.mk b/target/board/generic_x86_64/BoardConfig.mk
index 5105161..fda9e45 100755
--- a/target/board/generic_x86_64/BoardConfig.mk
+++ b/target/board/generic_x86_64/BoardConfig.mk
@@ -51,3 +51,5 @@
 BOARD_SEPOLICY_DIRS += \
         build/target/board/generic/sepolicy \
         build/target/board/generic_x86/sepolicy
+
+USE_CLANG_PLATFORM_BUILD := true