Update lit.py references to be relative to the new LLVM monorepo directory

This should fix recent CI failures on Pull Requests, which have been failing
due to failing to locate the `lit.py` script.

See this forum post describing the LLVM monorepo transition details:

https://forums.swift.org/t/llvm-monorepo-transition-happening-on-thursday-the-17th-of-october/29674

Author: stmontgomery

XCTest.xcodeproj/project.pbxproj

@@ -244,7 +244,7 @@
 			buildConfigurationList = DAA333B81C267AD6000CC115 /* Build configuration list for PBXLegacyTarget "SwiftXCTestFunctionalTests" */;
 			buildPhases = (
 			);
-			buildToolPath = "$(SRCROOT)/../llvm/utils/lit/lit.py";
+			buildToolPath = "$(SRCROOT)/../llvm-project/llvm/utils/lit/lit.py";
 			buildWorkingDirectory = "";
 			dependencies = (
 				DAA333BA1C267AF3000CC115 /* PBXTargetDependency */,

build_script.py

@@ -480,9 +480,9 @@ def main(args=sys.argv[1:]):
     build_parser.add_argument(
         "--test",
         help="Whether to run tests after building. Note that you must have "
-             "cloned https://github.com/apple/swift-llvm at {} in order to "
+             "cloned https://github.com/apple/llvm-project at {} in order to "
              "run this command.".format(os.path.join(
-                 os.path.dirname(SOURCE_DIR), 'llvm')),
+                 os.path.dirname(SOURCE_DIR), 'llvm-project')),
         action="store_true")
 
     test_parser = subparsers.add_parser(
@@ -502,7 +502,7 @@ def main(args=sys.argv[1:]):
         help="Path to the 'lit' tester tool used to run the test suite. "
              "'%(default)s' by default.",
         default=os.path.join(os.path.dirname(SOURCE_DIR),
-                             "llvm", "utils", "lit", "lit.py"))
+                             "llvm-project", "llvm", "utils", "lit", "lit.py"))
     test_parser.add_argument(
         "--foundation-build-dir",
         help="Path to swift-corelibs-foundation build products, which the "