[CMake] Use CMAKE_SYSROOT to build libs for Win to ARM cross tooolchain. NFC.

Provide CMAKE_SYSROOT for the libc++/libc++abi/libunwind libraries
instead of specific <foo>_SYSROOT for each of them.

Fixed passing some CMake arguments for the runtimes.

Referenced Differentials:
 * https://reviews.llvm.org/D119836
 * https://reviews.llvm.org/D112155
 * https://reviews.llvm.org/D111672

Differential Revision: https://reviews.llvm.org/D120383