(jm_PREREQ_ERROR): Do not invoke AC_CHECK_FUNCS with strerror_r, as

AC_FUNC_STRERROR_R does that.
Check for strerror declaration.

m4/error.m4

@@ -1,4 +1,4 @@
-#serial 3
+#serial 4
 
 dnl FIXME: put these prerequisite-only *.m4 files in a separate
 dnl directory -- otherwise, they'll conflict with existing files.
@@ -6,7 +6,8 @@ dnl directory -- otherwise, they'll conflict with existing files.
 dnl These are the prerequisite macros for GNU's error.c file.
 AC_DEFUN([jm_PREREQ_ERROR],
 [
-  AC_CHECK_FUNCS(strerror strerror_r vprintf doprnt)
+  AC_CHECK_FUNCS(strerror vprintf doprnt)
+  AC_CHECK_DECLS([strerror])
   AC_FUNC_STRERROR_R
   AC_HEADER_STDC
 ])