Initial stub of a Makefile and patches for LLVM

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

patches/llvm/0017-clang-use-as-needed-by-default.patch

@@ -0,0 +1,30 @@
+From eaf3a6393892bd36899f3ccb8782e7c6a06d6a8f Mon Sep 17 00:00:00 2001
+From: q66 <q66@chimera-linux.org>
+Date: Sun, 14 Apr 2024 14:48:51 +0200
+Subject: [PATCH 17/29] clang: use --as-needed by default
+
+---
+ clang/lib/Driver/ToolChains/Gnu.cpp | 7 +++++++
+ 1 file changed, 7 insertions(+)
+
+diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
+index f56eeda3c..5230be404 100644
+--- a/clang/lib/Driver/ToolChains/Gnu.cpp
++++ b/clang/lib/Driver/ToolChains/Gnu.cpp
+@@ -541,6 +541,13 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
+   bool NeedsSanitizerDeps = addSanitizerRuntimes(ToolChain, Args, CmdArgs);
+   bool NeedsXRayDeps = addXRayRuntime(ToolChain, Args, CmdArgs);
+   addLinkerCompressDebugSectionsOption(ToolChain, Args, CmdArgs);
++
++  // Use --as-needed by default for all explicit linker inputs on Linux
++  // We don't reset it afterwards because explicit argument does not
++  // get reset either (and that is permitted, so it should be fine)
++  if (Triple.isOSLinux())
++    CmdArgs.push_back("--as-needed");
++
+   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
+ 
+   addHIPRuntimeLibArgs(ToolChain, C, Args, CmdArgs);
+-- 
+2.49.0
+