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

[Vladimir Vereschaka via cfe-commits]

vvereschaka wrote:

@arichardson ,
works fine on the builders locally. Thank you.
Would yo merge these changes if they are ready?

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