Fix embedded (arm-none-eabi) builds

Due to OS#3360, build testing for arm-none-eabi was unfortunately
skipped for a long time.  This is a number of fixes that make the
compile test pass again.

Related: OS#3360
Change-Id: I88e3c8e1a8786ca2a6a023b0d27c74be200a8588
diff --git a/configure.ac b/configure.ac
index cb580a3..dd5f15b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -91,6 +91,8 @@
 CFLAGS="$saved_CFLAGS"
 AC_SUBST(SYMBOL_VISIBILITY)
 
+AC_CHECK_FUNCS(clock_gettime localtime_r)
+
 AC_DEFUN([CHECK_TM_INCLUDES_TM_GMTOFF], [
   AC_CACHE_CHECK(
     [whether struct tm has tm_gmtoff member],