configure.ac: check for pthread before librt

Works around a linker problem with some older glibc versions: if
"-lrt" was used, then "-pthread" was implied, but only the symbols
used by librt were available.  This led to a linker error because
pthread_atfork() was not found.

So with "-lrt", autoconf decides that no pthread flag is necessary,
but in the end fails due to pthread_atfork() missing.

By checking for pthread before librt, we avoid this dependency
problem.

configure.ac

@@ -193,6 +193,18 @@ dnl ---------------------------------------------------------------------------
 dnl Header/Library Checks
 dnl ---------------------------------------------------------------------------
 
+AX_PTHREAD
+LIBS="$PTHREAD_LIBS $LIBS"
+AM_CFLAGS="$AM_CFLAGS $PTHREAD_CFLAGS"
+AM_CXXFLAGS="$AM_CXXFLAGS $PTHREAD_CFLAGS"
+
+AC_CHECK_LIB([pthread], [pthread_setname_np],
+	[have_pthread_setname_np=yes],
+	[have_pthread_setname_np=no])
+if test x$have_pthread_setname_np = xyes; then
+	AC_DEFINE(HAVE_PTHREAD_SETNAME_NP, 1, [Is pthread_setname_np() available?])
+fi
+
 AC_SEARCH_LIBS([clock_gettime], [rt])
 
 AC_ARG_ENABLE(syslog,
@@ -229,18 +241,6 @@ AC_CHECK_HEADERS(valgrind/memcheck.h)
 
 AC_CHECK_HEADERS([sys/prctl.h], AC_CHECK_FUNCS([prctl]))
 
-AX_PTHREAD
-LIBS="$PTHREAD_LIBS $LIBS"
-AM_CFLAGS="$AM_CFLAGS $PTHREAD_CFLAGS"
-AM_CXXFLAGS="$AM_CXXFLAGS $PTHREAD_CFLAGS"
-
-AC_CHECK_LIB([pthread], [pthread_setname_np],
-	[have_pthread_setname_np=yes],
-	[have_pthread_setname_np=no])
-if test x$have_pthread_setname_np = xyes; then
-	AC_DEFINE(HAVE_PTHREAD_SETNAME_NP, 1, [Is pthread_setname_np() available?])
-fi
-
 dnl ---------------------------------------------------------------------------
 dnl Event loop selection
 dnl ---------------------------------------------------------------------------