[llvm] [llvm] Fix cmake string expansion in CrossCompile.cmake (PR #138901)

[David Truby via llvm-commits]

DavidTruby wrote:

This is necessary because CMake won't expand a list into string if the quoted string isn't surrounded by whitespace. If it is, it will correctly expand _and_ add quotes around the resulting string, so moving the string to cover the whole "-D..." option will make cmake do the right thing here.

https://github.com/llvm/llvm-project/pull/138901