Discover monotonic clock using compile-time check

monotonic clock check does not work when cross-compiling.

Upstream-Status: Denied [Does not work on OpenBSD]
Signed-off-by: Jussi Kukkonen <jussi.kukkonen@intel.com>


Original patch follows:

When xorg-xserver is being cross-compiled, there is currently no way
for us to detect whether the monotonic clock is available on the
target system, because we aren't able to run a test program on the host
system. Currently, in this situation, we default to not use the
monotonic clock. One problem with this situation is that the user will
be treated as idle when the date is updated.

To fix this situation, we now use a compile-time check to detect whether the
monotonic clock is available. This check can run just fine when we are
cross-compiling.

Signed-off-by: David James <davidjames at google.com>
---
 configure.ac | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/configure.ac b/configure.ac
index f7ab48c..26e85cd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1048,19 +1048,16 @@ if ! test "x$have_clock_gettime" = xno; then
         CPPFLAGS="$CPPFLAGS -D_POSIX_C_SOURCE=200112L"
     fi
 
-    AC_RUN_IFELSE([AC_LANG_SOURCE([
+    AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
 #include <time.h>
-
-int main(int argc, char *argv[[]]) {
-    struct timespec tp;
-
-    if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0)
+#include <unistd.h>
+int main() {
+#if !(defined(_POSIX_MONOTONIC_CLOCK) && _POSIX_MONOTONIC_CLOCK >= 0 && defined(CLOCK_MONOTONIC))
+        #error No monotonic clock
+#endif
         return 0;
-    else
-        return 1;
 }
-    ])], [MONOTONIC_CLOCK=yes], [MONOTONIC_CLOCK=no],
-       [MONOTONIC_CLOCK="cross compiling"])
+]])],[MONOTONIC_CLOCK=yes], [MONOTONIC_CLOCK=no])
 
     LIBS="$LIBS_SAVE"
     CPPFLAGS="$CPPFLAGS_SAVE"
-- 
2.1.4