Re-enabled constexpr tests

test/format-test.cc

@@ -2419,7 +2419,7 @@ TEST(FormatTest, FormatStringErrors) {
   EXPECT_ERROR_NOARGS("foo", FMT_NULL);
   EXPECT_ERROR_NOARGS("}", "unmatched '}' in format string");
   EXPECT_ERROR("{0:s", "unknown format specifier", Date);
-#  ifndef _MSC_VER
+#  if FMT_MSC_VER >= 1916
   // This causes an internal compiler error in MSVC2017.
   EXPECT_ERROR("{0:=5", "unknown format specifier", int);
   EXPECT_ERROR("{:{<}", "invalid fill character '{'", int);
@@ -2450,6 +2450,8 @@ TEST(FormatTest, FormatStringErrors) {
   EXPECT_ERROR("{:d}", "invalid type specifier", const char*);
   EXPECT_ERROR("{:d}", "invalid type specifier", std::string);
   EXPECT_ERROR("{:s}", "invalid type specifier", void*);
+#  else
+  fmt::print("warning: constexpr is broken in this versio of MSVC\n");
 #  endif
   EXPECT_ERROR("{foo", "compile-time checks don't support named arguments",
                int);