Bug 728968 - Detect clock_gettime when it's not in -lrt. r=khuey

configure.in

@@ -3728,20 +3728,23 @@ AC_CHECK_FUNCS(random strerror lchown fchmod snprintf statvfs memmove rint stat6
 AC_CHECK_FUNCS(flockfile getpagesize)
 AC_CHECK_FUNCS(localtime_r strtok_r)
 
-dnl check for clock_gettime(), the CLOCK_MONOTONIC clock, and -lrt
-_SAVE_LDFLAGS=$LDFLAGS
-LDFLAGS="$LDFLAGS -lrt"
-AC_CACHE_CHECK(for clock_gettime(CLOCK_MONOTONIC) and -lrt,
-               ac_cv_have_clock_monotonic,
-               [AC_TRY_LINK([#include <time.h>],
-                            [ struct timespec ts;
-                              clock_gettime(CLOCK_MONOTONIC, &ts); ],
-                            ac_cv_have_clock_monotonic=yes,
-                            ac_cv_have_clock_monotonic=no)])
-LDFLAGS=$_SAVE_LDFLAGS
-if test "$ac_cv_have_clock_monotonic" = "yes"; then
+dnl check for clock_gettime(), the CLOCK_MONOTONIC clock
+AC_CACHE_CHECK(for clock_gettime(CLOCK_MONOTONIC),
+               ac_cv_clock_monotonic,
+               [for libs in "" -lrt; do
+                    _SAVE_LDFLAGS="$LDFLAGS"
+                    LDFLAGS="$LDFLAGS $libs"
+                    AC_TRY_LINK([#include <time.h>],
+                                 [ struct timespec ts;
+                                   clock_gettime(CLOCK_MONOTONIC, &ts); ],
+                                 ac_cv_clock_monotonic=$libs
+                                 break,
+                                 ac_cv_clock_monotonic=no)
+                    LDFLAGS="$_SAVE_LDFLAGS"
+                done])
+if test "$ac_cv_clock_monotonic" != "no"; then
     HAVE_CLOCK_MONOTONIC=1
-    REALTIME_LIBS=-lrt
+    REALTIME_LIBS=$ac_cv_clock_monotonic
     AC_DEFINE(HAVE_CLOCK_MONOTONIC)
     AC_SUBST(HAVE_CLOCK_MONOTONIC)
     AC_SUBST(REALTIME_LIBS)