* gnu/packages/diffoscope.scm (diffoscope): Update to 186.
[source]: Add patch.
[arguments]: Add a new 'fix-failing-tests phase.
Don't explicitly return #t from phases.
* gnu/packages/patches/diffoscope-fix-test_item3_deflate_llvm_bitcode.patch:
New file.
* gnu/local.mk (dist_patch_DATA): Add it.
