Improve apple conditionals in filesystem.hpp

Two changes:
- (minor) Rename GHC_OS_MACOS -> GHC_OS_APPLE, since it is defined all apple platforms (iOS, watchOS, etc.), not just macOS.
- Changed the preprocessor conditional in last_write_time to align with its presumed intent. Previously, it would always have been true, which can't be intentional, because the *_OS_VERSION_MIN_REQUIRED is undefined and thus zero for platforms besides the current one, and therefore less than the constants--except for on very old SDKs where, e.g., MAC_OS_X_VERSION_10_13  and others would be undefined and therefore 0 and therefore making the clause false when it needed to be true. Therefore, I changed the conditions to be parallel to those in the dynamic selection headers, checking for the undefined, zero case and hardcoding the version values to support old SDKs.

Author: cpsauer

include/ghc/filesystem.hpp

@@ -36,7 +36,7 @@
 
 #ifndef GHC_OS_DETECTED
 #if defined(__APPLE__) && defined(__MACH__)
-#define GHC_OS_MACOS
+#define GHC_OS_APPLE
 #elif defined(__linux__)
 #define GHC_OS_LINUX
 #if defined(__ANDROID__)
@@ -164,7 +164,7 @@
 #include <langinfo.h>
 #endif
 #endif
-#ifdef GHC_OS_MACOS
+#ifdef GHC_OS_APPLE
 #include <Availability.h>
 #endif
 
@@ -4633,9 +4633,11 @@ GHC_INLINE void last_write_time(const path& p, file_time_type new_time, std::err
     if (!::SetFileTime(file.get(), 0, 0, &ft)) {
         ec = detail::make_system_error();
     }
-#elif defined(GHC_OS_MACOS) && \
-    (__MAC_OS_X_VERSION_MIN_REQUIRED < __MAC_10_13) || (__IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_11_0) || \
-    (__TV_OS_VERSION_MIN_REQUIRED < __TVOS_11_0) || (__WATCH_OS_VERSION_MIN_REQUIRED < __WATCHOS_4_0)
+#elif defined(GHC_OS_APPLE) && \
+    (__MAC_OS_X_VERSION_MIN_REQUIRED && __MAC_OS_X_VERSION_MIN_REQUIRED < 101300 \
+     || __IPHONE_OS_VERSION_MIN_REQUIRED && __IPHONE_OS_VERSION_MIN_REQUIRED < 110000 \
+     || __TV_OS_VERSION_MIN_REQUIRED && __TVOS_VERSION_MIN_REQUIRED < 110000 \
+     || __WATCH_OS_VERSION_MIN_REQUIRED && __WATCHOS_VERSION_MIN_REQUIRED < 40000)
     struct ::stat fs;
     if (::stat(p.c_str(), &fs) == 0) {
         struct ::timeval tv[2];