look for clock_gettime() in libc first, then in librt if not found.

CMakeLists.txt

@@ -1617,14 +1617,14 @@ elseif(UNIX AND NOT APPLE AND NOT RISCOS AND NOT HAIKU)
   CheckPTHREAD()
 
   if(SDL_CLOCK_GETTIME)
-    check_library_exists(rt clock_gettime "" FOUND_CLOCK_GETTIME_LIBRT)
-    if(FOUND_CLOCK_GETTIME_LIBRT)
-      list(APPEND EXTRA_LIBS rt)
+    check_library_exists(c clock_gettime "" FOUND_CLOCK_GETTIME_LIBC)
+    if(FOUND_CLOCK_GETTIME_LIBC)
       set(HAVE_CLOCK_GETTIME 1)
     else()
-      check_library_exists(c clock_gettime "" FOUND_CLOCK_GETTIME_LIBC)
-      if(FOUND_CLOCK_GETTIME_LIBC)
+      check_library_exists(rt clock_gettime "" FOUND_CLOCK_GETTIME_LIBRT)
+      if(FOUND_CLOCK_GETTIME_LIBRT)
         set(HAVE_CLOCK_GETTIME 1)
+        list(APPEND EXTRA_LIBS rt)
       endif()
     endif()
   endif()

configure

@@ -28404,14 +28404,14 @@ else $as_nop
 fi
 
     if test x$enable_clock_gettime = xyes; then
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for clock_gettime in -lrt" >&5
-printf %s "checking for clock_gettime in -lrt... " >&6; }
-if test ${ac_cv_lib_rt_clock_gettime+y}
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for clock_gettime in -lc" >&5
+printf %s "checking for clock_gettime in -lc... " >&6; }
+if test ${ac_cv_lib_c_clock_gettime+y}
 then :
   printf %s "(cached) " >&6
 else $as_nop
   ac_check_lib_save_LIBS=$LIBS
-LIBS="-lrt  $LIBS"
+LIBS="-lc  $LIBS"
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -28429,17 +28429,17 @@ return clock_gettime ();
 _ACEOF
 if ac_fn_c_try_link "$LINENO"
 then :
-  ac_cv_lib_rt_clock_gettime=yes
+  ac_cv_lib_c_clock_gettime=yes
 else $as_nop
-  ac_cv_lib_rt_clock_gettime=no
+  ac_cv_lib_c_clock_gettime=no
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.beam \
     conftest$ac_exeext conftest.$ac_ext
 LIBS=$ac_check_lib_save_LIBS
 fi
-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ac_cv_lib_rt_clock_gettime" >&5
-printf "%s\n" "$ac_cv_lib_rt_clock_gettime" >&6; }
-if test "x$ac_cv_lib_rt_clock_gettime" = xyes
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ac_cv_lib_c_clock_gettime" >&5
+printf "%s\n" "$ac_cv_lib_c_clock_gettime" >&6; }
+if test "x$ac_cv_lib_c_clock_gettime" = xyes
 then :
   have_clock_gettime=yes
 fi
@@ -28448,16 +28448,15 @@ fi
 
 printf "%s\n" "#define HAVE_CLOCK_GETTIME 1" >>confdefs.h
 
-            EXTRA_LDFLAGS="$EXTRA_LDFLAGS -lrt"
         else
-            { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for clock_gettime in -lc" >&5
-printf %s "checking for clock_gettime in -lc... " >&6; }
-if test ${ac_cv_lib_c_clock_gettime+y}
+            { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for clock_gettime in -lrt" >&5
+printf %s "checking for clock_gettime in -lrt... " >&6; }
+if test ${ac_cv_lib_rt_clock_gettime+y}
 then :
   printf %s "(cached) " >&6
 else $as_nop
   ac_check_lib_save_LIBS=$LIBS
-LIBS="-lc  $LIBS"
+LIBS="-lrt  $LIBS"
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -28475,26 +28474,26 @@ return clock_gettime ();
 _ACEOF
 if ac_fn_c_try_link "$LINENO"
 then :
-  ac_cv_lib_c_clock_gettime=yes
+  ac_cv_lib_rt_clock_gettime=yes
 else $as_nop
-  ac_cv_lib_c_clock_gettime=no
+  ac_cv_lib_rt_clock_gettime=no
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.beam \
     conftest$ac_exeext conftest.$ac_ext
 LIBS=$ac_check_lib_save_LIBS
 fi
-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ac_cv_lib_c_clock_gettime" >&5
-printf "%s\n" "$ac_cv_lib_c_clock_gettime" >&6; }
-if test "x$ac_cv_lib_c_clock_gettime" = xyes
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ac_cv_lib_rt_clock_gettime" >&5
+printf "%s\n" "$ac_cv_lib_rt_clock_gettime" >&6; }
+if test "x$ac_cv_lib_rt_clock_gettime" = xyes
 then :
   have_clock_gettime=yes
 fi
 
             if test x$have_clock_gettime = xyes; then
+                EXTRA_LDFLAGS="$EXTRA_LDFLAGS -lrt"
 
 printf "%s\n" "#define HAVE_CLOCK_GETTIME 1" >>confdefs.h
 
-               EXTRA_LDFLAGS="$EXTRA_LDFLAGS"
             fi
         fi
     fi

configure.ac

@@ -3681,15 +3681,14 @@ CheckClockGettime()
 [AS_HELP_STRING([--enable-clock_gettime], [use clock_gettime() instead of gettimeofday() on UNIX [default=yes]])],
                   , enable_clock_gettime=yes)
     if test x$enable_clock_gettime = xyes; then
-        AC_CHECK_LIB(rt, clock_gettime, have_clock_gettime=yes)
+        AC_CHECK_LIB(c, clock_gettime, have_clock_gettime=yes)
         if test x$have_clock_gettime = xyes; then
-            AC_DEFINE(HAVE_CLOCK_GETTIME, 1, [ ])
-            EXTRA_LDFLAGS="$EXTRA_LDFLAGS -lrt"
+           AC_DEFINE(HAVE_CLOCK_GETTIME, 1, [ ])
         else
-            AC_CHECK_LIB(c, clock_gettime, have_clock_gettime=yes)
+            AC_CHECK_LIB(rt, clock_gettime, have_clock_gettime=yes)
             if test x$have_clock_gettime = xyes; then
-               AC_DEFINE(HAVE_CLOCK_GETTIME, 1, [ ])
-               EXTRA_LDFLAGS="$EXTRA_LDFLAGS"
+                EXTRA_LDFLAGS="$EXTRA_LDFLAGS -lrt"
+                AC_DEFINE(HAVE_CLOCK_GETTIME, 1, [ ])
             fi
         fi
     fi