GCC 7.3 complains that this is not a compile time constant.

test/format-test.cc: In member function ‘virtual void FormatTest_FormatStringErrors_Test::TestBody()’:
test/format-test.cc:1919:3: error: non-constant condition for static assertion
   static_assert(test_error<__VA_ARGS__>(fmt, error), "")
   ^
test/format-test.cc:1924:3: note: in expansion of macro ‘EXPECT_ERROR’
   EXPECT_ERROR("{0:s", "unknown format specifier", Date);
   ^~~~~~~~~~~~