Import GNU Make 4.4.1

Landlock Make hasn't been working well on AARCH64 systems. Let's do this
over the right way, using our new build tools.

third_party/make/mkcustom.h

@@ -0,0 +1,65 @@
+/* Miscellaneous global declarations and portability cruft for GNU Make.
+Copyright (C) 2023 Free Software Foundation, Inc.
+This file is part of GNU Make.
+
+GNU Make is free software; you can redistribute it and/or modify it under the
+terms of the GNU General Public License as published by the Free Software
+Foundation; either version 3 of the License, or (at your option) any later
+version.
+
+GNU Make is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along with
+this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/*
+  This file is included at the end of config.h
+
+   That means it's included _everywhere_ as the first thing,
+   INCLUDING content imported from gnulib.  BE AWARE!!
+*/
+
+#undef  HAVE_CONFIG_H
+#define HAVE_CONFIG_H 1
+
+/* Specify we want GNU source code.  This must be defined before any
+   system headers are included.  */
+
+#define _GNU_SOURCE 1
+
+/* AIX requires this to be the first thing in the file.  */
+#if HAVE_ALLOCA_H
+# include <alloca.h>
+#else
+# ifdef _AIX
+ #pragma alloca
+# else
+#  if !defined(__GNUC__) && !defined(WINDOWS32)
+#   ifndef alloca /* predefined by HP cc +Olibcalls */
+char *alloca ();
+#   endif
+#  endif
+# endif
+#endif
+
+/* Declare function prototypes for src/misc.c functions if needed.  */
+
+#include <stddef.h>
+
+#if !HAVE_STRCASECMP && !HAVE_STRICMP && !HAVE_STRCMPI
+int strcasecmp (const char *s1, const char *s2);
+#endif
+
+#if !HAVE_STRNCASECMP && !HAVE_STRNICMP && !HAVE_STRNCMPI
+int strncasecmp (const char *s1, const char *s2, size_t n);
+#endif
+
+#if !HAVE_MEMPCPY
+void *mempcpy (void *dest, const void *src, size_t n);
+#endif
+
+#if !HAVE_STPCPY
+char *stpcpy (char *dest, const char *src);
+#endif