mrustc: init

This contains some extraordinarily ugly hacks for a set of even uglier
Makefiles.

Signed-off-by: Ophestra <cat@gensokyo.uk>

mrustc/0001-do-not-download-rustc.patch

@@ -1,7 +1,7 @@
 From 157772049aa7da13533026292cb4f67c1e8bf542 Mon Sep 17 00:00:00 2001
 From: nobody <nobody@localhost>
 Date: Sun, 19 Jul 2026 06:21:49 +0900
-Subject: [PATCH 1/2] do not download rustc
+Subject: [PATCH 1/3] do not download rustc
 
 The $(RUSTC_SRC_DL) file already exists, but for some reason Make wants
 to rebuild this target when it has $(RUSTC_SRC_TARBALL) as a dependency.

mrustc/0002-Revert-HIR-Typecheck-Optimise-by-doing-multiple-chec.patch

@@ -1,7 +1,7 @@
 From 6e66feb3b6ae698c3d29211847c71c00f87fbf78 Mon Sep 17 00:00:00 2001
 From: nobody <nobody@localhost>
 Date: Sun, 19 Jul 2026 06:23:12 +0900
-Subject: [PATCH 2/2] Revert "HIR Typecheck - Optimise by doing multiple checks
+Subject: [PATCH 2/3] Revert "HIR Typecheck - Optimise by doing multiple checks
  per pass"
 
 This reverts commit 99d9bd0c788b0c72fc2f4fee6187a462ceb059f2.

mrustc/package.az

@@ -12,6 +12,7 @@ package mrustc-source {
 	patches = [
 		"0001-do-not-download-rustc.patch",
 		"0002-Revert-HIR-Typecheck-Optimise-by-doing-multiple-chec.patch",
+		"0003-rustc-src-enable-rustix-use-libc-feature-revert-port.patch",
 
 		"remove-git-invocations.patch",
 	];