abuild: remove libc specific logic
Last use of the '!libc_*' option has been removed in 61cb57cda98. libpthread special casing only triggers on uclibc (which we don't use anymore).
Edited by Sertonix
Last use of the '!libc_*' option has been removed in 61cb57cda98. libpthread special casing only triggers on uclibc (which we don't use anymore).