[Lit] Fix to prevent creation of "%SystemDrive%" directory on Windows.

[andrewng]

Summary

This patch propogates the environment variable SYSTEMDRIVE on Windows when
running the unit tests. This prevents the creation of a directory named
"%SystemDrive%" when running the unit tests from FileSystemTest that use the
function llvm::sys::fs::remove_directories which in turn uses SHFileOperationW.
It is within SHFileOperationW that this environment variable may be used and if
undefined causes the creation of a "%SystemDrive%" directory in the current
directory.

[zturner]

I don't disbelieve you, but do you have any thoughts about why I've never seen this when running tests locally?

[andrewng]

In D32910#747152, @zturner wrote:

I don't disbelieve you, but do you have any thoughts about why I've never seen this when running tests locally?

Yes, this is a bit of a strange one. It has only started happening fairly recently (a week or 2), so we suspect that it might be a Windows change that's triggered it. I'm running on Windows 10 Pro x64 1607 build 14393.1066.

[rnk]

lgtm

test/Unit/lit.cfg

for symbolizer in ['ASAN_SYMBOLIZER_PATH', 'MSAN_SYMBOLIZER_PATH']:
     if symbolizer in os.environ:
         config.environment[symbolizer] = os.environ[symbolizer]
 
 # Win32 seeks DLLs along %PATH%.
 if sys.platform in ['win32', 'cygwin'] and os.path.isdir(config.shlibdir):
     config.environment['PATH'] = os.path.pathsep.join((
             config.shlibdir, config.environment['PATH']))
 
+# Win32 may use %SYSTEMDRIVE% during file system shell operations, so propogate.
+if sys.platform == 'win32' and 'SYSTEMDRIVE' in os.environ:
+    config.environment['SYSTEMDRIVE'] = os.environ['SYSTEMDRIVE']
+
 ###
 
 # Check that the object root is known.
 if config.test_exec_root is None:
     # Otherwise, we haven't loaded the site specific configuration (the user is
     # probably trying to run on a test file directly, and either the site
     # configuration hasn't been created by the build system, or we are in an
     # out-of-tree build situation).