Move arm target to clang by default.

Bug: 23163853
Change-Id: I4cb95ed652ca697461e2fb22811779aa2df8d262
diff --git a/target/board/generic/BoardConfig.mk b/target/board/generic/BoardConfig.mk
index 4e5504e..b1cefca 100644
--- a/target/board/generic/BoardConfig.mk
+++ b/target/board/generic/BoardConfig.mk
@@ -81,3 +81,5 @@
   # include an expanded selection of fonts for the SDK.
   EXTENDED_FONT_FOOTPRINT := true
 endif
+
+USE_CLANG_PLATFORM_BUILD := true