[gnumeric] configure: insist on c99.

[Morten Welinder <mortenw src gnome org>]

commit c6557361a4d387c7f6a6c65a10bc0c6a6d25d9ef
Author: Morten Welinder <terra gnome org>
Date:   Tue Dec 8 21:38:24 2015 -0500

    configure: insist on c99.
    
    It's 2015.

 ChangeLog    |    4 ++++
 configure.ac |    5 +++++
 2 files changed, 9 insertions(+), 0 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 6d1f120..281713c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2015-12-08  Morten Welinder  <terra gnome org>
+
+       * configure.ac (CC): Insist on c99.
+
 2015-12-05  Morten Welinder  <terra gnome org>
 
        * src/sf-dpq.c (prayleigh, qrayleigh): New functions.
diff --git a/configure.ac b/configure.ac
index 10a2c06..abdb868 100644
--- a/configure.ac
+++ b/configure.ac
@@ -79,6 +79,11 @@ AC_CANONICAL_HOST
 
 AC_ISC_POSIX
 AC_PROG_CC
+AC_PROG_CC_C99
+if test "$ac_cv_prog_cc_c99" = no; then
+       AC_MSG_ERROR([*** c99 is required])
+fi
+
 AC_PROG_YACC
 AM_PROG_LEX
 AC_PROG_LN_S