[SYCLomatic][BUG][LIT] Modified llvm-lit framework to accept case insensitive value for BUILD_LIT (#2744)

Author: TejaX-Alaghari

clang/test/lit.cfg.py

@@ -349,7 +349,7 @@ def calculate_arch_features(arch_string):
     config.available_features.add("llvm-driver")
 
 #SYCLomatic Code
-if "BUILD_LIT" in os.environ and os.environ["BUILD_LIT"] == 'TRUE':
+if os.getenv("BUILD_LIT", "").lower() == 'true':
     config.available_features.add("build_lit")
 #End SYCLomatic