external/llvmx

LLVM sources already exist as an external project on Android (external/llvm), at version 3.6. This is problematic:

• very old version, with limited capabilities
• there is no way to make it compile with c++11/ART (runtime and compiler).
• it is used as an external library to other components of AOSP, so it cannot be removed or updated

The workaround for this is to create another external project: external/llvmx, which is based on llvm10. It does not conflict with the other llvm library, and it can generate libLLVM.so. This work well with AOSP as it is compiled with the SOONG toolchain (compiling libLLVM.so externally won't)

Other generated tools:

• llc
• opt
• llvm-link

Other notes

pull_includes.sh:

This was invoked once to fetch the generated headers from a remote machine: ./device (scp from remote cross-compiled sources)
./device/arm
./device/arm64

./host
./host/darwin_x86_64 (cp from local machine - macbook)

pull_tlbgen.sh:

This was invoked once to copy the tblgen inc headers for:
./include/tblgen

Those aux headers had to be created with custom targets through the SOONG build system, i.e., by modifying:
./Android.bp
./soong/tblgen.go

This was a lot of work, so they were generated and imported (as pre-builts) from an external compilation.