(jm_AC_PREREQ_XSTRTOUMAX): Check whether

<inttypes.h> defines strtoumax as a macro (and not as a
function).

m4/xstrtoumax.m4

@@ -1,4 +1,4 @@
-#serial 1
+#serial 2
 
 # autoconf tests required for use of xstrtoumax.c
 
@@ -7,14 +7,26 @@ AC_DEFUN(jm_AC_PREREQ_XSTRTOUMAX,
   AC_REQUIRE([jm_AC_HEADER_INTTYPES_H])
   AC_REQUIRE([jm_AC_TYPE_UNSIGNED_LONG_LONG])
   AC_CHECK_HEADERS(stdlib.h)
-  AC_REPLACE_FUNCS(strtoumax)
+
+  AC_CACHE_CHECK([whether <inttypes.h> defines strtoumax as a macro],
+    jm_cv_func_strtoumax_macro,
+    AC_EGREP_CPP([inttypes_h_defines_strtoumax], [#include <inttypes.h>
+#ifdef strtoumax
+ inttypes_h_defines_strtoumax
+#endif],
+      jm_cv_func_strtoumax_macro=yes,
+      jm_cv_func_strtoumax_macro=no))
+
+  if test "$jm_cv_func_strtoumax_macro" != yes; then
+    AC_REPLACE_FUNCS(strtoumax)
+  fi
 
   dnl We don't need (and can't compile) the replacement strtoull
   dnl unless the type `unsigned long long' exists.
   dnl Also, only the replacement strtoumax invokes strtoull,
   dnl so we need the replacement strtoull only if strtoumax does not exist.
-  case "$ac_cv_type_unsigned_long_long,$ac_cv_func_strtoumax" in
-    yes,no)
+  case "$ac_cv_type_unsigned_long_long,$jm_cv_func_strtoumax_macro,$ac_cv_func_strtoumax" in
+    yes,no,no)
       AC_REPLACE_FUNCS(strtoull)
       ;;
   esac