[llvm] [llvm-objcopy] Check for missing argument values (PR #70710)

[via llvm-commits]

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+## An error must be reported if a required argument value is missing.
+# RUN: not llvm-objcopy --only-section 2>&1 | FileCheck --check-prefix=CHECK-NO-VALUE %s
+# RUN: not llvm-objcopy -O 2>&1 | FileCheck --check-prefix=CHECK-NO-VALUE %s
+# CHECK-NO-VALUE: error: argument to '{{.*}}' is missing
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quic-akaryaki wrote:

I am using a wildcard to reuse one pattern for several (two) different options. The point of this test is to verify that the message gets printed. I think there is enough context in the message to avoid misidentification for other messages.
I am not checking if the message is exactly the same because I don't see it as a realistic possibility. 
I don't think a random corruption in the output is likely, and testing for it would be outside of the scope of this test.

https://github.com/llvm/llvm-project/pull/70710