(jm_AC_PREREQ_XSTRTOUMAX): Quote first arg of AC_DEFUN.

Require jm_AC_TYPE_INTMAX_T and jm_AC_TYPE_LONG_LONG since they
is needed to parse the include file.
Simplify logic behind the args to AC_REPLACE.

m4/xstrtoumax.m4

@@ -2,9 +2,11 @@
 
 # autoconf tests required for use of xstrtoumax.c
 
-AC_DEFUN(jm_AC_PREREQ_XSTRTOUMAX,
+AC_DEFUN([jm_AC_PREREQ_XSTRTOUMAX],
 [
+  AC_REQUIRE([jm_AC_TYPE_INTMAX_T])
   AC_REQUIRE([jm_AC_TYPE_UINTMAX_T])
+  AC_REQUIRE([jm_AC_TYPE_LONG_LONG])
   AC_REQUIRE([jm_AC_TYPE_UNSIGNED_LONG_LONG])
   AC_CHECK_DECLS([strtoul, strtoull])
   AC_CHECK_HEADERS(limits.h stdlib.h inttypes.h)
@@ -22,20 +24,17 @@ AC_DEFUN(jm_AC_PREREQ_XSTRTOUMAX,
     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 "$ac_cv_type_unsigned_long_long,$jm_cv_func_strtoumax_macro,$ac_cv_func_strtoumax" in
-    yes,no,no)
-      AC_REPLACE_FUNCS(strtoull strtol)
-      ;;
-  esac
-
+  dnl Only the replacement strtoumax invokes strtoul and strtoull,
+  dnl so we need the replacements only if strtoumax does not exist.
   case "$jm_cv_func_strtoumax_macro,$ac_cv_func_strtoumax" in
     no,no)
-      AC_REPLACE_FUNCS(strtoul strtol)
+      AC_REPLACE_FUNCS(strtoul)
+
+      dnl We don't need (and can't compile) the replacement strtoull
+      dnl unless the type `unsigned long long' exists.
+      if test "$ac_cv_type_unsigned_long_long" = yes; then
+	AC_REPLACE_FUNCS(strtoull)
+      fi
       ;;
   esac
-
 ])