Do not make std::filesystem::path hash available for macOS <10.15

C++17 <filesystem> is only available on macOS 10.15 and newer, so
do not enable this feature on older versions.

PiperOrigin-RevId: 638348906
Change-Id: I5e12db47513f7f8aeb9e55a3e253c866ec046d47

absl/hash/internal/hash.h

@@ -599,7 +599,9 @@ H AbslHashValue(H hash_state, std::basic_string_view<Char> str) {
 #if defined(__cpp_lib_filesystem) && __cpp_lib_filesystem >= 201703L && \
     !defined(_LIBCPP_HAS_NO_FILESYSTEM_LIBRARY) && \
     (!defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__) ||        \
-     __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ >= 130000)
+     __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ >= 130000) &&       \
+    (!defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) ||         \
+     __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101500)
 
 #define ABSL_INTERNAL_STD_FILESYSTEM_PATH_HASH_AVAILABLE 1