[COMMITTED] configure.ac: Update AC_PROG_CC for autoconf 2.70

[Mark Wielaard]

With autoconf 2.70 we must use AC_PROG_CC (which will check for
c11 and c99), for earlier versions we'll use AC_PROG_CC_C99.

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 configure.ac | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 6704dc0..c887aed 100644
--- a/configure.ac
+++ b/configure.ac
@@ -41,7 +41,7 @@ AC_USE_SYSTEM_EXTENSIONS
 # Checks for programs.
 AC_PROG_AWK
 AC_PROG_SED
-AC_PROG_CC_C99
+m4_version_prereq([2.70], [AC_PROG_CC], [AC_PROG_CC_C99])
 AC_PROG_LN_S
 AC_CHECK_TOOL([LD], [ld])
 AC_CHECK_TOOL([READELF], [readelf])
-- 
2.31.1