Enable UPX compression for Windows binaries

Compress Windows LLVM binaries with UPX in order to decrease our distribution package size.

Back to LLVM 13.0.1

The recent bump to LLVM 14 is causing problems with the Mono AOT compiler, so for the time being we're going back to 13.0.1.
The only difference between this release and L_13.0.1-4.0.1 is that we now include Windows PDB files in the archive.

Bump to LLVM 14.0.1 + include Windows PDB files

Upgrades the LLVM version to the just-released 14.0.1 version (changes) and enables creating Windows PDB files for all the binaries.

Add llc to the toolchain

The toolchain now includes llc (the LLVM IR to object file/assembler compiler) which will eventually be used by Xamarin.Android.

Testing phase of llvm-based mingw toolchain

This release is created from the llvm-mingw branch (PR) which at some point will be merged into main but for now it remains in a separate branch. This release is purely for Xamarin.Android test purposes, it should not be used for anything else at this point.

Drop GNU Binutils entirely

We've decided to use only LLVM for all the tools, thus replacing the gold linker from GNU Binutils with lld from LLVM.

First release of LLVM-based toolchain

The toolchain uses llvm-mc, llvm-strip/objdump from LLVM and the gold linker from Binutils. It also contains a gas wrapper around llvm-mc so that Mono/dotnet AOT can work without any changes.

Fix ARM32 builds

ARM32 builds need to target ARMv7-a

Fixes for ARM32 and Windows wrapper scripts

• ARM32 should accept Thumb instructions now
• Windows wrapper scripts (.cmd) quote their paths

A handful of fixes for Windows

Fix process creation on Windows