[Clang][Test] Add llvm-lto, llvm-lto2 and llvm-profdata to the tool substitutions list

Similar to issue fixed in D107155, some lit tests invoke `llvm-lto`,
`llvm-lto2` and `llvm-profdata` without going through the substitution
system. While the test runner correctly picks up these binaries from
the build directory, it doesn't print its absolute path. When copying
the invocations when reproducing test failures, this can result in
`command not found: llvm-lto` or other errors (caused by using wrong
version of the tool).

This patch adds these tools to the `tools` variable in
`clang/test/lit.cfg.py` which will then call add_tool_substitutions.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D143806