[libcxx] r324385 - Fix building libc++ with the macOS 10.13 SDK with -mmacosx-version-min=10.12 or lower.

[Nico Weber via cfe-commits]

Author: nico
Date: Tue Feb  6 11:17:41 2018
New Revision: 324385

URL: http://llvm.org/viewvc/llvm-project?rev=324385&view=rev
Log:
Fix building libc++ with the macOS 10.13 SDK with -mmacosx-version-min=10.12 or lower.

The 10.13 SDK always defines utimensat() (with an availability(macosx=10.13) annotation)
and unconditionally defines UTIME_OMIT, so use the compile-time availability macros
on Apple platforms instead.

For people statically linking libc++, it might make sense to also provide an opt-in
option for using __builtin_available() to dynamically check for the OS version,
but for now let's do the smallest thing needed to unbreak the build.

Based on a patch by Eric Fiselier <eric at efcs.ca>: https://reviews.llvm.org/D34249
Fixes PR33469.

Modified:
    libcxx/trunk/src/experimental/filesystem/operations.cpp

Modified: libcxx/trunk/src/experimental/filesystem/operations.cpp
URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/src/experimental/filesystem/operations.cpp?rev=324385&r1=324384&r2=324385&view=diff
==============================================================================
--- libcxx/trunk/src/experimental/filesystem/operations.cpp (original)
+++ libcxx/trunk/src/experimental/filesystem/operations.cpp Tue Feb  6 11:17:41 2018
@@ -21,7 +21,34 @@
 #include <sys/stat.h>
 #include <sys/statvfs.h>
 #include <fcntl.h>  /* values for fchmodat */
-#if !defined(UTIME_OMIT)
+
+#if (__APPLE__)
+#if defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__)
+#if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101300
+#define _LIBCXX_USE_UTIMENSAT
+#endif
+#elif defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__)
+#if __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ >= 110000
+#define _LIBCXX_USE_UTIMENSAT
+#endif
+#elif defined(__ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__)
+#if __ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__ >= 110000
+#define _LIBCXX_USE_UTIMENSAT
+#endif
+#elif defined(__ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__)
+#if __ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__ >= 40000
+#define _LIBCXX_USE_UTIMENSAT
+#endif
+#endif // __ENVIRONMENT_.*_VERSION_MIN_REQUIRED__
+#else
+// We can use the presence of UTIME_OMIT to detect platforms that provide
+// utimensat.
+#if defined(UTIME_OMIT)
+#define _LIBCXX_USE_UTIMENSAT
+#endif
+#endif // __APPLE__
+
+#if !defined(_LIBCXX_USE_UTIMENSAT)
 #include <sys/time.h> // for ::utimes as used in __last_write_time
 #endif
 
@@ -560,9 +587,7 @@ void __last_write_time(const path& p, fi
     using namespace std::chrono;
     std::error_code m_ec;
 
-    // We can use the presence of UTIME_OMIT to detect platforms that do not
-    // provide utimensat.
-#if !defined(UTIME_OMIT)
+#if !defined(_LIBCXX_USE_UTIMENSAT)
     // This implementation has a race condition between determining the
     // last access time and attempting to set it to the same value using
     // ::utimes