Delete MSVC intermediate files on "make clean" from tests.

lld-link shells out to MSVC for certain types of work, and this
results in some MSVC output files being generated even though
clang / lld are the compiler / linker.  This is expected, so we
make sure to clean these output files on make clean.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@224345 91177308-0d34-0410-b5e6-96231b3b80d8