[clang] [runtimes] Fix parsing of LIB{CXX, CXXABI, UNWIND}_TEST_PARAMS (PR #67691)

[Alexander Richardson via cfe-commits]

arichardson wrote:

@vvereschaka I tested this locally by adding a parameter with quotes to my CMake invocation, so it should hopefully work. Could you please test if this fixes the builder?

https://github.com/llvm/llvm-project/pull/67691