New file, defining jm_FUNC_MBRTOWC.

m4/mbrtowc.m4

@@ -0,0 +1,19 @@
+#serial 1
+
+dnl From Paul Eggert
+
+AC_DEFUN(jm_FUNC_MBRTOWC,
+[
+  AC_MSG_CHECKING([whether mbrtowc and mbstate_t are properly declared])
+  AC_CACHE_VAL(jm_cv_func_mbrtowc,
+    [AC_TRY_LINK(
+       [#include <wchar.h>],
+       [mbstate_t state; return ! (sizeof state && mbrtowc);],
+       [jm_cv_func_mbrtowc=yes],
+       [jm_cv_func_mbrtowc=no])])
+  if test $jm_cv_func_mbrtowc = yes; then
+    AC_MSG_RESULT(yes)
+    AC_DEFINE(HAVE_MBRTOWC, 1,
+      [Define to 1 if mbrtowc and mbstate_t are properly declared.])
+  fi
+])