Lines such as

258: validate_local_permissions failed: (127) Failed to parse PKCS7 SMIME document: 281473198688096:error:21075075:PKCS7 routines:PKCS7_verify:certificate verify error:../crypto/pkcs7/pk7_smime.c:284:Verify error:self signed certificate

from cyclonedds security tests are matching the Jenkins analysis model regexp as a Clang warning.

Linux aarch64 debug #1234 is an example build exhibiting these warnings.

I've done some quick checking to see if there's a described format for clang messages in order to improve upstream's regexp and haven't found anything yet. Since our normal Linux builds use GCC we don't necessarily need to look at them for Clang errors so I'm going to open a PR that adds that parser only conditionally.

This is related to #316