use do-while-false in FOLLY_SAFE_CHECK

Summary: To avoid the marginal but still unnecessary compile-time cost of constructing a lambda. And enclose the full thing in braces so it can be used in an unbraced `if`.

Reviewed By: ot, luciang

Differential Revision: D27817005

fbshipit-source-id: 9a1a6e0389fea5907a3a20cffbd6a029b0a85eb9

folly/lang/SafeAssert.h

@@ -32,12 +32,13 @@
 #endif
 
 #define FOLLY_DETAIL_SAFE_CHECK_IMPL(d, p, expr, expr_s, ...)     \
+  do {                                                            \
     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_CHECK_LINKAGE constexpr ::folly::detail::safe_assert_arg \
-        __folly_detail_safe_assert_arg{                                        \
+      FOLLY_DETAIL_SAFE_CHECK_LINKAGE constexpr ::folly::detail:: \
+          safe_assert_arg __folly_detail_safe_assert_arg{         \
               FOLLY_PP_STRINGIZE(expr_s),                         \
               __FILE__,                                           \
               __LINE__,                                           \
@@ -48,7 +49,7 @@
       ::folly::detail::safe_assert_terminate<p>(                  \
           __folly_detail_safe_assert_arg, __VA_ARGS__);           \
     }                                                             \
-  [] {}()
+  } while (false)
 
 //  FOLLY_SAFE_CHECK
 //