[test] Fix append_path in the empty case

[fjricci]

Summary

normpath() was being called on an empty string and appended to
the environment variable in the case where the environment variable
was unset. This led to ":." being appended to the path, since
normpath() of an empty string is '.', presumably to represent cwd.

[fjricci]

fix append_path

utils/lit/lit/llvm/config.py

def __init__(self, lit_config, config):
         # Check if we should run long running tests.
         long_tests = lit_config.params.get("run_long_tests", None)
         if lit.util.pythonize_bool(long_tests):
             features.add("long_tests")
 
         if target_triple:
             if re.match(r'^x86_64.*-apple', target_triple):
                 if 'address' in sanitizers:
-                    self.with_environment('ASAN_OPTIONS', 'detect_leaks=1', append_path=True)
+                    self.with_environment('ASAN_OPTIONS', 'detect_leaks=1')
             if re.match(r'^x86_64.*-linux', target_triple):
                 features.add("x86_64-linux")
             if re.match(r'.*-win32$', target_triple):
                 features.add('target-windows')
 
         use_gmalloc = lit_config.params.get('use_gmalloc', None)
         if lit.util.pythonize_bool(use_gmalloc):
             # Allow use of an explicit path for gmalloc library.