[llvm-objcopy][test] Add cmp after copy

[keith]

Summary

All of the other tests here either check that the copy fails, or that
the resulting binary is the same, it seems like this check was omitted
for the universal object case.

[MaskRay]

Looks great!

[steven_wu]

This breaks darwin bot: https://green.lab.llvm.org/green/job/clang-stage1-RA/29421/

Can you take a look or revert if you can't address it immediately? Thanks!

[paulkirth]

We're also seeing this on Fuchsia's Clang CI. https://luci-milo.appspot.com/ui/p/fuchsia/builders/toolchain.ci/clang-mac-x64/b8813965072418331409/overview

[smeenai]

We're seeing an internal failure after this change as well :( Great catch, but it looks like it exposed some existing brokenness.

[keith]

Yea it passes on my M1 machine, I will test on Intel and see if that's the difference, I have reverted since so hopefully everyone is back to green and I'll debug async and post here with the new fix.

llvm/test/tools/llvm-objcopy/MachO/universal-object.test

 # RUN: llvm-lipo %t.universal.containing.archive.copy -thin i386 -output %t.archive.i386.copy
 # RUN: llvm-lipo %t.universal.containing.archive.copy -thin x86_64 -output %t.archive.x86_64.copy
 # RUN: cmp %t.archive.i386 %t.archive.i386.copy
 # RUN: cmp %t.x86_64 %t.archive.x86_64.copy
 
 ## Case 3: copy an archive containing a universal object.
 # RUN: llvm-ar cr %t.archive.containing.universal %t.universal
 # RUN: llvm-objcopy %t.archive.containing.universal %t.archive.containing.universal.copy
+# RUN: cmp %t.archive.containing.universal %t.archive.containing.universal.copy
 
 ## Case 4: try to copy a universal object file contaning a bitcode slice.
 # RUN: echo 'target triple = "arm64-apple-ios8.0.0"' | llvm-as -o %t.bitcode
 # RUN: llvm-lipo %t.bitcode  %t.x86_64 -create -output %t.universal.containing.bitcode
 # RUN: not llvm-objcopy %t.universal.containing.bitcode %t.universal.containing.bitcode.copy 2>&1 \
 # RUN:  | FileCheck --check-prefix=UNSUPPORTED_UNIVERSAL_OBJECT %s
 
 ## Case 5: try to copy an archive containing an unsupported universal object.
 # RUN: llvm-ar cr %t.archive.universal.bitcode %t.universal.containing.bitcode
 # RUN: not llvm-objcopy %t.archive.universal.bitcode %t.archive.universal.bitcode.copy 2>&1 \
 # RUN:  | FileCheck --check-prefix=UNSUPPORTED_UNIVERSAL_OBJECT %s
 
 # VERIFY_ARCHS: i386 x86_64
 # UNSUPPORTED_UNIVERSAL_OBJECT: slice for 'arm64' of the universal Mach-O binary {{.*}} is not a Mach-O object or an archive