`stl-lit` refuses to run tests using small drive letter in test path

[AlexGuteniev]

Describe the bug

stl-lit refuses to run tests using small drive letter in test path.
The drive letter is used from current directory for relative paths without drive letter, or if it is resent in the path from the path iself.

Command-line test case

Absolute path

C:\Project\STL\out\x64>"C:\Program Files\Python312\python" tests\utils\stl-lit\stl-lit.py c:\Project\STL\tests\std\tests\VSO_0157762_feature_test_macros
stl-lit.py: C:\Project\STL\llvm-project\llvm\utils\lit\lit\discovery.py:276: warning: input 'c:\\Project\\STL\\tests\\std\\tests\\VSO_0157762_feature_test_macros' contained no tests
error: did not discover any tests for provided path(s)

C:\Project\STL\out\x64>"C:\Program Files\Python312\python" tests\utils\stl-lit\stl-lit.py C:\Project\STL\tests\std\tests\VSO_0157762_feature_test_macros
-- Testing: 35 tests, 12 workers --
PASS: std :: tests/VSO_0157762_feature_test_macros:00 (1 of 35)

.
.
.
PASS: std :: tests/VSO_0157762_feature_test_macros:16 (35 of 35)

Testing Time: 1.65s

Total Discovered Tests: 35
  Unsupported:  4 (11.43%)
  Passed     : 31 (88.57%)

C:\Project\STL\out\x64>

Relative path

C:\Project\STL\out\x64>cd \

C:\>cd/d c:\Project\STL\out\x64

c:\Project\STL\out\x64>"C:\Program Files\Python312\python" tests\utils\stl-lit\stl-lit.py ..\..\tests\std\tests\VSO_0157762_feature_test_macros
stl-lit.py: C:\Project\STL\llvm-project\llvm\utils\lit\lit\discovery.py:276: warning: input '..\\..\\tests\\std\\tests\\VSO_0157762_feature_test_macros' contained no tests
error: did not discover any tests for provided path(s)

c:\Project\STL\out\x64>cd \

c:\>cd/d C:\Project\STL\out\x64

C:\Project\STL\out\x64>"C:\Program Files\Python312\python" tests\utils\stl-lit\stl-lit.py ..\..\tests\std\tests\VSO_0157762_feature_test_macros
-- Testing: 35 tests, 12 workers --
PASS: std :: tests/VSO_0157762_feature_test_macros:00 (1 of 35)
.
.
.
PASS: std :: tests/VSO_0157762_feature_test_macros:16 (35 of 35)

Testing Time: 1.57s

Total Discovered Tests: 35
  Unsupported:  4 (11.43%)
  Passed     : 31 (88.57%)

C:\Project\STL\out\x64>

Expected behavior

Either any drive letter is accepted, or this problem is explained in readme.md

STL version

bd3d740

[StephanTLavavej]

I believe I have a fix.