+# gl_PROG_CC_C99
+# Modifies the value of the shell variable CC in an attempt to make $CC
+# understand ISO C99 source code.
+# This is like AC_PROG_CC_C99, except that
+# - AC_PROG_CC_C99 did not exist in Autoconf versions < 2.60,
+# - AC_PROG_CC_C99 does not mix well with AC_PROG_CC_STDC
+# <http://lists.gnu.org/archive/html/bug-gnulib/2011-09/msg00367.html>,
+# but many more packages use AC_PROG_CC_STDC than AC_PROG_CC_C99
+# <http://lists.gnu.org/archive/html/bug-gnulib/2011-09/msg00441.html>.
+# Remaining problems:
+# - When AC_PROG_CC_STDC is invoked twice, it adds the C99 enabling options
+# to CC twice
+# <http://lists.gnu.org/archive/html/bug-gnulib/2011-09/msg00431.html>.
+# - AC_PROG_CC_STDC is likely to change when C1X is an ISO standard.
+AC_DEFUN([gl_PROG_CC_C99],
+[
+ dnl Change that version number to the minimum Autoconf version that supports
+ dnl mixing AC_PROG_CC_C99 calls with AC_PROG_CC_STDC calls.
+ m4_version_prereq([9.0],
+ [AC_REQUIRE([AC_PROG_CC_C99])],
+ [AC_REQUIRE([AC_PROG_CC_STDC])])
+])
+