[llvm-mca] Add llvm-mca to the standard toolchain installer / release package

[RKSimon]

As discussed here: https://discourse.llvm.org/t/where-can-i-get-llvm-mca

llvm-mca is user facing enough that it should probably be treated as part of the toolchain and not just as an internal tool

We need it to be added to LLVM_TOOLCHAIN_TOOLS

[llvmbot]

@llvm/issue-subscribers-tools-llvm-mca

Author: Simon Pilgrim (RKSimon)

As discussed here: https://discourse.llvm.org/t/where-can-i-get-llvm-mca

llvm-mca is user facing enough that it should probably be treated as part of the toolchain and not just as an internal tool

We need it to be added to LLVM_TOOLCHAIN_TOOLS

[RKSimon]

@tru Would it be acceptable to add this to the 17.x branch so that it gets added to 17.x release packages?