The libc-common class despite being called libc-commmon is specific to glibc and only used by one recipe in oe-core (glibc). Lets move the contents into the glibc recipe and remove the class.
https://layers.openembedded.org/layerindex/branch/master/recipes/?q=inherits%3Alibc-common shows that its just glibc in oe-core and a glibc fork in meta-linaro that use this class.
Patch on the list.
Merged in a0bff0db1eeb128776757d5f3d0bc1ebdc135498