MIPS: clear_cache, use _flush_cache instead of cacheflush

The cacheflush is only defined with __USE_MISC, which depends on _DEFAULT_SOURCE,
_GNU_SOURCE or _BSD_SOURCE, or _SVID_SOURCE.

If CC is called with -std=c11, these macros won't be defined, Let's use
_flush_cache, which is defined always.

Reviewed By: brad, jrtc27

Differential Revision: https://reviews.llvm.org/D156072

(cherry picked from commit 0f99bc2)

Author: wzssyqa

compiler-rt/lib/builtins/clear_cache.c

@@ -113,7 +113,7 @@ void __clear_cache(void *start, void *end) {
 #elif defined(__linux__) || defined(__OpenBSD__)
     // Pre-R6 may not be globalized. And some implementations may give strange
     // synci_step. So, let's use libc call for it.
-    cacheflush(start, end_int - start_int, BCACHE);
+    _flush_cache(start, end_int - start_int, BCACHE);
 #else
     (void)start_int;
     (void)end_int;