Improvements to stopwatch implementation

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index a1c9e42..68077a9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -55,8 +55,9 @@
 	IF(WIN32)
 		TARGET_LINK_LIBRARIES(${target} ws2_32)
 	ELSEIF(CMAKE_SYSTEM_NAME MATCHES "(Solaris|SunOS)")
-		TARGET_LINK_LIBRARIES(${target} socket nsl rt)
-	ELSE()
+		TARGET_LINK_LIBRARIES(${target} socket nsl)
+	ENDIF()
+	IF(NOT APPLE AND NOT WIN32)
 		TARGET_LINK_LIBRARIES(${target} rt)
 	ENDIF()
 	IF(THREADSAFE)

src/timing.c

diff --git a/src/timing.c b/src/timing.c
index cf729ea..3125678 100644
--- a/src/timing.c
+++ b/src/timing.c
@@ -99,8 +99,14 @@
 
 int git_stopwatch_start(git_stopwatch *s)
 {
-	if (clock_gettime(CLOCK_MONOTONIC, &s->start)) {
-		giterr_set(GITERR_OS, "Unable to get the monotonic timer");
+	s->clk_id = GIT_PREFERRED_CLOCK;
+
+	/* On EINVAL for the preferred clock, fall back to CLOCK_REALTIME */
+	if (clock_gettime(s->clk_id, &s->start) &&
+		(CLOCK_REALTIME == GIT_PREFERRED_CLOCK || errno != EINVAL ||
+		 clock_gettime(s->clk_id = CLOCK_REALTIME, &s->start))) {
+		giterr_set(GITERR_OS, "Unable to read the clock");
+		s->running = 0;
 		return -1;
 	}
 
@@ -119,8 +125,8 @@
 		return -1;
 	}
 
-	if (clock_gettime(CLOCK_MONOTONIC, &end)) {
-		giterr_set(GITERR_OS, "Unable to get the monotonic timer");
+	if (clock_gettime(s->clk_id, &end)) {
+		giterr_set(GITERR_OS, "Unable to read the clock");
 		return -1;
 	}
 
@@ -145,4 +151,4 @@
 	return 0;
 }
 
-#endif
\ No newline at end of file
+#endif

src/timing.h

diff --git a/src/timing.h b/src/timing.h
index 6ee631a..3dc18f4 100644
--- a/src/timing.h
+++ b/src/timing.h
@@ -35,8 +35,17 @@
 
 #else
 
+/* On systems which support CLOCK_MONOTONIC, prefer it
+ * over CLOCK_REALTIME */
+#ifdef CLOCK_MONOTONIC
+# define GIT_PREFERRED_CLOCK CLOCK_MONOTONIC
+#else
+# define GIT_PREFERRED_CLOCK CLOCK_REALTIME
+#endif
+
 typedef struct git_stopwatch {
 	struct timespec start;
+	clockid_t clk_id;
 	unsigned running : 1;
 } git_stopwatch;