Parameterize use of clang in libc_ndk.

We still have issues with clang coverage in static libraries, so we
need to make sure we follow suit with the rest of libc for now.

Bug: 17574078
Change-Id: I2ab58a84b1caa0d8d08415d240c35adec5b1e150
diff --git a/libc/Android.mk b/libc/Android.mk
index b5e4899..7dc7cbf 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -1123,7 +1123,7 @@
 include $(CLEAR_VARS)
 
 LOCAL_MODULE := libc_ndk
-LOCAL_CLANG := true
+LOCAL_CLANG := $(use_clang)
 LOCAL_ASFLAGS := $(LOCAL_CFLAGS)
 LOCAL_CONLYFLAGS := $(libc_common_conlyflags)
 LOCAL_CFLAGS := $(libc_common_cflags) -fvisibility=hidden -O0