Fix clang build.

Apparently clang really doesn't want you to take the address of a builtin.
Since this is only a temporary hack, let's just shrug and accept that
clang-built volantis images won't work until we have new NVIDIA blobs.

Bug: http://b/20065774
Change-Id: I4c8e893b15a1af8f9c54d3f89bfef112b63d09b4
diff --git a/libc/arch-arm64/bionic/libgcc_compat.c b/libc/arch-arm64/bionic/libgcc_compat.c
index 35158ce..904cc16 100644
--- a/libc/arch-arm64/bionic/libgcc_compat.c
+++ b/libc/arch-arm64/bionic/libgcc_compat.c
@@ -1,5 +1,7 @@
 /* STOPSHIP: remove this once the flounder blobs have been rebuilt (http://b/20065774). */
 
+#if defined(__clang__)
+
 extern void __clear_cache(char*, char*);
 extern char _Unwind_Backtrace;
 extern char _Unwind_GetIP;
@@ -9,3 +11,5 @@
     &_Unwind_Backtrace,
     &_Unwind_GetIP,
 };
+
+#endif