[clang] [llvm] [Utils] Add new --update-tests flag to llvm-lit (PR #108425)

[Nicolai Hähnle via cfe-commits]

================
@@ -2,3 +2,15 @@ config.substitutions = list(config.substitutions)
 config.substitutions.insert(
     0, (r"%clang\b", """*** Do not use the driver in Sema tests. ***""")
 )
+
+if lit_config.update_tests:
+    import sys
+    import os
+
+    curdir = os.path.dirname(os.path.realpath(__file__))
+    testdir = os.path.dirname(curdir)
+    clangdir = os.path.dirname(testdir)
+    utilspath = os.path.join(clangdir, "utils")
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nhaehnle wrote:

I believe this can be simplified to `os.path.join(clangdir, "..", "..", "utils")`?

https://github.com/llvm/llvm-project/pull/108425