Use LLDB_SRC for relative paths

[beanz]

Summary

Going from LLDB_SRC instead of the file path is safer when looking for compiler-rt. Also need to add support for looking inside the LLVM runtimes subdirectory.

Eventually we should just get CMake to provide these paths during configuration.

[tfiala]

(Retro) LGTM.

lldb/trunk/packages/Python/lldbsuite/test/decorators.py

return skipTestIfFn(
             api_levels,
             archs))
 
 
 def skipUnlessCompilerRt(func):
     """Decorate the item to skip tests if testing remotely."""
     def is_compiler_rt_missing():
         compilerRtPath = os.path.join(
-            os.path.dirname(__file__),
-            "..",
+            os.environ["LLDB_SRC"],
             "..",
             "..",
             "..",
             "llvm",
             "projects",
             "compiler-rt")
+        if not os.path.exists(compilerRtPath):
+            compilerRtPath = os.path.join(
+            os.environ["LLDB_SRC"],
+            "..",
+            "..",
+            "..",
+            "llvm",
+            "runtimes",
+            "compiler-rt")
         return "compiler-rt not found" if not os.path.exists(
             compilerRtPath) else None
     return skipTestIfFn(is_compiler_rt_missing)(func)
 
 
 def skipUnlessThreadSanitizer(func):
     """Decorate the item to skip test unless Clang -fsanitize=thread is supported."""