disassembly inspection functions for FOLLY_SAFE_CHECK

Summary: Add some functions that can be used to inspect the generated code for `FOLLY_SAFE_CHECK` and `FOLLY_SAFE_PCHECK`.

Reviewed By: swolchok

Differential Revision: D26996102

fbshipit-source-id: 257f59d5904c319ed01e55cfd75939b41e55c53d

folly/lang/test/SafeAssertTest.cpp

@@ -20,8 +20,21 @@
 
 #include <folly/Benchmark.h>
 #include <folly/Conv.h>
+#include <folly/lang/Keep.h>
 #include <folly/portability/GTest.h>
 
+extern "C" FOLLY_ATTR_WEAK void sink();
+
+extern "C" FOLLY_KEEP void check_folly_safe_check(bool cond) {
+  FOLLY_SAFE_CHECK(cond, "the condition failed");
+  sink();
+}
+
+extern "C" FOLLY_KEEP void check_folly_safe_pcheck(bool cond) {
+  FOLLY_SAFE_PCHECK(cond, "the condition failed");
+  sink();
+}
+
 // clang-format off
 [[noreturn]] void fail() {
   FOLLY_SAFE_CHECK(0 + 0, "hello");