[tsan] #undef one-letter macros

buildgo.sh puts most of sanitizer_common together in a single source
file. These single-letter macros end up affecting a lot of unrelated
code; #undef them as early as possible.

llvm-svn: 353902

compiler-rt/lib/tsan/rtl/tsan_md5.cc

@@ -138,6 +138,14 @@ static const void *body(MD5_CTX *ctx, const void *data, ulong_t size) {
   return ptr;
 }
 
+#undef F
+#undef G
+#undef H
+#undef I
+#undef STEP
+#undef SET
+#undef GET
+
 void MD5_Init(MD5_CTX *ctx) {
   ctx->a = 0x67452301;
   ctx->b = 0xefcdab89;