Initial stub of a Makefile and patches for LLVM

Nothing much, but getting some patches from chimera linux that should
work.

patches/llvm/0026-clang-implicitly-include-stdc-predef.h.patch

@@ -0,0 +1,41 @@
+From c5c9ef16fd4a48f1131d319497fa16473f88d4da Mon Sep 17 00:00:00 2001
+From: q66 <q66@chimera-linux.org>
+Date: Sun, 14 Apr 2024 14:55:21 +0200
+Subject: [PATCH 26/29] clang: implicitly include stdc-predef.h
+
+This behavior is required to match gcc and get default access
+to some macros to get rid of certain hacks (especially on musl,
+which does not explicitly include this - glibc includes it from
+features.h)
+
+Inspired by https://reviews.llvm.org/D137043 but this should not
+be tied to libc choice, as gcc unconditionally does the preinclude
+for both.
+---
+ clang/lib/Driver/ToolChains/Clang.cpp | 10 ++++++++++
+ 1 file changed, 10 insertions(+)
+
+diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
+index 417b85899..2e583c39c 100644
+--- a/clang/lib/Driver/ToolChains/Clang.cpp
++++ b/clang/lib/Driver/ToolChains/Clang.cpp
+@@ -1168,6 +1168,16 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
+     }
+   }
+ 
++  // Follow gcc in pre-including stdc-predef.h in non-freestanding mode
++  // Has to be done this early so that it comes before user-supplied -includes
++  if (!Args.hasArg(options::OPT_nostdinc) &&
++      !Args.hasArg(options::OPT_nostdlibinc) &&
++      !Args.hasArg(options::OPT_ffreestanding) &&
++      getToolChain().getTriple().isOSLinux()) {
++    CmdArgs.push_back("-include");
++    CmdArgs.push_back("stdc-predef.h");
++  }
++
+   bool RenderedImplicitInclude = false;
+   for (const Arg *A : Args.filtered(options::OPT_clang_i_Group)) {
+     if (A->getOption().matches(options::OPT_include) &&
+-- 
+2.49.0
+