[clang] [clang] Fix a segfault when M is a nullptr (PR #130712)

[via cfe-commits]

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@@ -0,0 +1,35 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+
+// There are two requirements here to result in the owner of a macro being null.
+// 1) There must be a configuration mismatch between a header and a file it depends on
+// 2) -fmodules-local-submodule-visibility must be enabled.
+
+// Unfortunately, libcxx is compiled with exceptions, but the sysroot it depends on is likely compiled without exceptions.
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cor3ntin wrote:

The comment is not relevant to the test; can you remove it? 

https://github.com/llvm/llvm-project/pull/130712