Run the min/max tests agaist the header <charconv>. Fix that header so it passes. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@345352 91177308-0d34-0410-b5e6-96231b3b80d8

include/charconv

@@ -87,6 +87,9 @@ namespace std {
 #pragma GCC system_header
 #endif
 
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace __itoa {
@@ -609,4 +612,6 @@ from_chars(const char* __first, const char* __last, _Tp& __value, int __base)
 
 _LIBCPP_END_NAMESPACE_STD
 
+_LIBCPP_POP_MACROS
+
 #endif  // _LIBCPP_CHARCONV

test/libcxx/min_max_macros.sh.cpp

@@ -46,6 +46,8 @@ TEST_MACROS();
 TEST_MACROS();
 #include <cfloat>
 TEST_MACROS();
+#include <charconv>
+TEST_MACROS();
 #include <chrono>
 TEST_MACROS();
 #include <cinttypes>