[libunwind] [runtimes] Remove explicit -isysroot from the testing configurations on macOS (PR #66265)

[Louis Dionne via cfe-commits]

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@@ -2,6 +2,24 @@
 
 @SERIALIZED_LIT_PARAMS@
 
+# Workaround for https://gitlab.kitware.com/cmake/cmake/-/issues/19180.
+#
+# On Apple platforms, CMake resolves the compiler to the final binary using
+# `$(xcrun --find <compiler>`). Unfortunately, running this compiler as-is
+# doesn't work because it doesn't have knowledge of the SDK root. To work
+# around that, we transform the resolved compiler back to the corresponding
+# /usr/bin shim if we can.
+def workaround_cmake_issue_on_Apple(cxx):
----------------
ldionne wrote:

This workaround doesn't change anything non-Apple platforms. `xcrun` doesn't exist, so the whole thing will throw an exception and we just use the `cxx` that was provided by CMake directly (i.e. `CMAKE_CXX_COMPILER`).

By the way, this increases the "test as we ship" on Apple platforms because people on Apple platforms don't run `/path/to/compiler -isysroot <whatever>`, they run `clang++` directly and that shim takes care of setting the `SDKROOT` environment variable which tells Clang where to look for. If the CMake issue linked in the comment were fixed, none of this would be necessary.

https://github.com/llvm/llvm-project/pull/66265