macOS/glog: Silence syscall deprecation warning

Upstream will release the fix in 0.6 which will take time.
Silence two warnings.

Differential Revision: https://developer.blender.org/D11246

extern/glog/README.blender

@@ -7,3 +7,4 @@ Local modifications:
   checks for functions and so are needed.
 * Added special definitions of HAVE_SNPRINTF and HAVE_LIB_GFLAGS
   in Windows' specific config.h.
+* Silenced syscall deprecation warnings on macOS >= 10.12.

extern/glog/src/raw_logging.cc

@@ -59,7 +59,7 @@
 # include <unistd.h>
 #endif
 
-#if defined(HAVE_SYSCALL_H) || defined(HAVE_SYS_SYSCALL_H)
+#if (defined(HAVE_SYSCALL_H) || defined(HAVE_SYS_SYSCALL_H)) && (!(defined OS_MACOSX))
 # define safe_write(fd, s, len)  syscall(SYS_write, fd, s, len)
 #else
   // Not so safe, but what can you do?

extern/glog/src/utilities.cc

@@ -259,7 +259,13 @@ pid_t GetTID() {
 #endif
   static bool lacks_gettid = false;
   if (!lacks_gettid) {
+#ifdef OS_MACOSX
+    uint64_t tid64;
+    const int error = pthread_threadid_np(NULL, &tid64);
+    pid_t tid = error ? -1 : (pid_t)tid64;
+#else
     pid_t tid = syscall(__NR_gettid);
+#endif
     if (tid != -1) {
       return tid;
     }