__PRETTY_FUNCTION__ -> __func__ in FOLLY_SAFE_CHECK

Summary:
Storing the `__PRETTY_FUNCTION__` for logging has an unreasonable cost on (non-strippable) binary size for debug builds, as different template instantiation will produce long, demangled, and non-mergeable strings.

If necessary, all the information is retrievable from the debug info (even if the function is inlined), where it's stored in much more efficient form. So, switch to `__func__`, which is stripped.

Reviewed By: yfeldblum, luciang

Differential Revision: D27825136

fbshipit-source-id: d499084c7e7b24db1cd46aa2b03f4a590c6eddc3

folly/lang/SafeAssert.h

@@ -36,7 +36,7 @@
     if ((!d || ::folly::kIsDebug || ::folly::kIsSanitize) &&      \
         !static_cast<bool>(expr)) {                               \
       FOLLY_DETAIL_SAFE_CHECK_LINKAGE constexpr auto              \
-          __folly_detail_safe_assert_fun = __PRETTY_FUNCTION__;   \
+          __folly_detail_safe_assert_fun = __func__;              \
       FOLLY_DETAIL_SAFE_CHECK_LINKAGE constexpr ::folly::detail:: \
           safe_assert_arg __folly_detail_safe_assert_arg{         \
               FOLLY_PP_STRINGIZE(expr_s),                         \