Add library checking for clock_gettime() support

acinclude.m4

@@ -1814,6 +1814,82 @@ AC_DEFUN([TYPE_IN_ADDR_T],
   ]) dnl AC_CHECK_TYPE
 ]) dnl AC_DEFUN
 
+dnl CURL_CHECK_LIBS_CLOCK_GETTIME
+dnl -------------------------------------------------
+dnl Check for libraries needed for clock_gettime,
+dnl and prepended to LIBS any needed libraries.
+
+AC_DEFUN([CURL_CHECK_LIBS_CLOCK_GETTIME], [
+  AC_REQUIRE([AC_HEADER_TIME])dnl
+  AC_CHECK_HEADERS(sys/types.h sys/time.h time.h)
+  #
+  AC_MSG_CHECKING([for clock_gettime in libraries])
+  #
+  curl_cv_save_LIBS="$LIBS"
+  curl_cv_gclk_LIBS="unknown"
+  #
+  for x_xlibs in '' '-lrt' '-lposix4' ; do
+    if test -z "$x_xlibs"; then
+      LIBS="$curl_cv_save_LIBS"
+    else
+      LIBS="$x_xlibs $curl_cv_save_LIBS"
+    fi
+    AC_LINK_IFELSE([
+      AC_LANG_PROGRAM([
+#undef inline
+#ifdef HAVE_SYS_TYPES_H
+#include <sys/types.h>
+#endif
+#ifdef HAVE_SYS_TIME_H
+#include <sys/time.h>
+#ifdef TIME_WITH_SYS_TIME
+#include <time.h>
+#endif
+#else
+#ifdef HAVE_TIME_H
+#include <time.h>
+#endif
+#endif
+      ],[
+        (void)clock_gettime(0, 0);
+      ])
+    ],[
+       curl_cv_gclk_LIBS="$x_xlibs"
+       break
+    ])
+  done
+  #
+  LIBS="$curl_cv_save_LIBS"
+  #
+  case X-"$curl_cv_gclk_LIBS" in
+    X-unknown)
+      AC_MSG_RESULT([cannot find clock_gettime])
+      ac_cv_func_clock_gettime="no"
+      ;;
+    X-)
+      AC_MSG_RESULT([no additional lib required])
+      ac_cv_func_clock_gettime="yes"
+      ;;
+    *)
+      if test -z "$curl_cv_save_LIBS"; then
+        LIBS="$curl_cv_gclk_LIBS"
+      else
+        LIBS="$curl_cv_gclk_LIBS $curl_cv_save_LIBS"
+      fi
+      AC_MSG_RESULT([$curl_cv_gclk_LIBS])
+      ac_cv_func_clock_gettime="yes"
+      ;;
+  esac
+  #
+  case "$ac_cv_func_clock_gettime" in
+    yes)
+      AC_DEFINE_UNQUOTED(HAVE_CLOCK_GETTIME, 1,
+        [Define to 1 if you have the clock_gettime function.])
+      ;;
+  esac
+  #
+]) dnl AC_DEFUN
+
 dnl ************************************************************
 dnl check for "localhost", if it doesn't exist, we can't do the
 dnl gethostbyname_r tests!