[LLDB] Make API tests to run using MSYS tools

MSYS 'uname' on windows returns "MSYS_NT*" instead of windows32 and also
MSYS 'pwd' returns non-windows path string.
This patch fixes Makefile.rules to make adjustments required to run LLDB
API tests using MSYS tools.

Differential Revision: https://reviews.llvm.org/D133002