cli: use mach_absolute_time as fallback for clock_gettime on darwin. Fixes #283

clock_gettime() is only available since MacOS X 10.12 (Sierra).
diff --git a/tools/dav1d.c b/tools/dav1d.c
index 598755c..5e6afb9 100644
--- a/tools/dav1d.c
+++ b/tools/dav1d.c
@@ -27,6 +27,7 @@
 
 #include "config.h"
 #include "vcs_version.h"
+#include "cli_config.h"
 
 #include <assert.h>
 #include <errno.h>
@@ -44,6 +45,9 @@
 #ifdef _WIN32
 # include <windows.h>
 #endif
+#if defined(HAVE_MACH_ABSOLUTE_TIME)
+#include <mach/mach_time.h>
+#endif
 
 #include "dav1d/dav1d.h"
 
@@ -60,10 +64,14 @@
     LARGE_INTEGER t;
     QueryPerformanceCounter(&t);
     return 1000000000 * t.QuadPart / frequency.QuadPart;
-#else
+#elif defined(HAVE_CLOCK_GETTIME)
     struct timespec ts;
     clock_gettime(CLOCK_MONOTONIC, &ts);
     return 1000000000ULL * ts.tv_sec + ts.tv_nsec;
+#elif defined(HAVE_MACH_ABSOLUTE_TIME)
+    mach_timebase_info_data_t info;
+    mach_timebase_info(&info);
+    return mach_absolute_time() * info.numer / info.denom;
 #endif
 }
 
diff --git a/tools/meson.build b/tools/meson.build
index 9f9356d..5b942b3 100644
--- a/tools/meson.build
+++ b/tools/meson.build
@@ -31,16 +31,26 @@
     subdir_done()
 endif
 
+
+# Configuratin data for cli_config.h
+cli_cdata = configuration_data()
+
 rt_dependency = []
 if host_machine.system() != 'windows'
-    if not cc.has_function('clock_gettime', prefix : '#include <time.h>', args : test_args)
+    if cc.has_function('clock_gettime', prefix : '#include <time.h>', args : test_args)
+        cli_cdata.set('HAVE_CLOCK_GETTIME', 1)
+    elif host_machine.system() == 'darwin'
+        cli_cdata.set('HAVE_MACH_ABSOLUTE_TIME', 1)
+    else
         rt_dependency = cc.find_library('rt', required: false)
         if not cc.has_function('clock_gettime', prefix : '#include <time.h>', args : test_args, dependencies : rt_dependency)
             error('clock_gettime not found')
         endif
+        cli_cdata.set('HAVE_CLOCK_GETTIME', 1)
     endif
 endif
 
+cli_config_h_target = configure_file(output: 'cli_config.h', configuration: cli_cdata)
 
 # dav1d cli tool sources
 dav1d_sources = files(
@@ -58,7 +68,7 @@
 
 dav1d = executable('dav1d',
     dav1d_sources,
-    rev_target,
+    rev_target, cli_config_h_target,
 
     link_with : libdav1d,
     include_directories : [dav1d_inc_dirs],