[clang] [libc++][lit] Allow overriding the executor for tests (PR #66545)

[Vladimir Vereschaka via cfe-commits]

vvereschaka wrote:

[executorfix.diff.txt](https://github.com/llvm/llvm-project/files/12745676/executorfix.diff.txt)

@arichardson ,

here is few updates for your fix (please see attached file):
* added an escaping of quotes for the serialized lit parameter. There could be an executor string something like that `"C:/Python310/python.exe" "C:/buildbot/temp/llvm-project/libcxx/utils/ssh.py" --host=ubuntu at jetson6.lab.llvm.org`. We need to replace `"` with `\"` because it goes into the python's string.
* the test parameters are processing as a cmake list. We need to properly prepare `xxx_LIBxxx_TEST_PARAMS` variables in the cmake cache file.

The `libunwind` and `libc++abi` tests are passed successfully with these changes. I have started the `libc++` tests. It will take about 1 hour, but they already started successfully. These changes are working properly on the win cross toolchain builders.

https://github.com/llvm/llvm-project/pull/66545