[llvm] MC: Use reportFatalUsageError for COFF with non-windows (PR #147911)

[Fangrui Song via llvm-commits]

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@@ -0,0 +1,5 @@
+; RUN: not llc -mtriple=aarch64-unknown-linux-coff -filetype=null %s 2>&1 | FileCheck %s
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MaskRay wrote:

This can be merged into the other unsupported object file format test you are adding. Perhaps rename the test if necessary.

https://github.com/llvm/llvm-project/pull/147911