1 files changed, 28 insertions, 0 deletions
diff --git a/build/m4/ax_c__generic.m4 b/build/m4/ax_c__generic.m4
new file mode 100644
index 000000000..0c4dd52c6
--- /dev/null
+++ b/build/m4/ax_c__generic.m4
@@ -0,0 +1,28 @@
+# https://lists.gnu.org/archive/html/autoconf-commit/2012-12/msg00004.html
+# AC_C__GENERIC
+# -------------
+# Define HAVE_C__GENERIC if _Generic works, a la C11.
+AN_IDENTIFIER([_Generic], [AC_C__GENERIC])
+AC_DEFUN([AC_C__GENERIC],
+[AC_CACHE_CHECK([for _Generic], ac_cv_c__Generic,
+[AC_COMPILE_IFELSE(
+   [AC_LANG_SOURCE(
+      [[int
+        main (int argc, char **argv)
+        {
+          int a = _Generic (argc, int: argc = 1);
+          int *b = &_Generic (argc, default: argc);
+          char ***c = _Generic (argv, int: argc, default: argv ? &argv : 0);
+          _Generic (1 ? 0 : b, int: a, default: b) = &argc;
+          _Generic (a = 1, default: a) = 3;
+          return a + !b + !c;
+        }
+      ]])],
+   [ac_cv_c__Generic=yes],
+   [ac_cv_c__Generic=no])])
+if test $ac_cv_c__Generic = yes; then
+  AC_DEFINE([HAVE_C__GENERIC], 1,
+           [Define to 1 if C11-style _Generic works.])
+fi
+])# AC_C__GENERIC
+