Avoid redundant declaration of static constexpr members in c++17

Keep declarations in c++ < 17 using new macro, GTEST_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL.

Fixes #4148.

PiperOrigin-RevId: 511510401
Change-Id: I76c3f2fccf07a0978adcbe5f8f0203b9d0c33872

Author: dinord

googletest/include/gtest/internal/gtest-internal.h

@@ -900,8 +900,10 @@ class HasDebugStringAndShortDebugString {
       HasDebugStringType::value && HasShortDebugStringType::value;
 };
 
+#ifdef GTEST_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 template <typename T>
 constexpr bool HasDebugStringAndShortDebugString<T>::value;
+#endif
 
 // When the compiler sees expression IsContainerTest<C>(0), if C is an
 // STL-style container class, the first overload of IsContainerTest

googletest/include/gtest/internal/gtest-port.h

@@ -2447,4 +2447,9 @@ using Variant = ::std::variant<T...>;
 #endif  // __has_include
 #endif  // GTEST_HAS_ABSL
 
+#if defined(GTEST_INTERNAL_CPLUSPLUS_LANG) && \
+    GTEST_INTERNAL_CPLUSPLUS_LANG < 201703L
+#define GTEST_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL 1
+#endif
+
 #endif  // GOOGLETEST_INCLUDE_GTEST_INTERNAL_GTEST_PORT_H_