d/patches: Add pthread to glslang.pc for OSDependent
It appears that autopkgtest is still preventing migration of glslang 11:
https://qa.debian.org/excuses.php?package=glslang
https://ci.debian.net/data/autopkgtest/testing/amd64/g/glslang/10407405/log.gz
I tested this with sbuild using the --run-autopkgtest parameter.