[llvm] [objcopy] Return an error in case of an invalid regex (PR #74319)

[James Henderson via llvm-commits]

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+## Test if providing objcopy with an invalid regex generates an error.
+
+# RUN: yaml2obj %s -o %t
+
+# RUN: not llvm-objcopy --regex --strip-symbol='f[^)' %t /dev/null 2>&1 | FileCheck %s
+# CHECK: cannot compile regular expression
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jh7370 wrote:

Please include the regex pattern and "error:" prefix in the message matching, to show that a) it is an error, not a warning, and b) that the pattern is formatted as expected.

https://github.com/llvm/llvm-project/pull/74319