[Libc] add non-standard header 'err.h'

headers/header_spec.txt

share/libc/__fc_libc.h

share/libc/argz.c

share/libc/err.h

tests/libc/err_h.c

tests/libc/fc_libc.c

tests/libc/oracle/argz_c.res.oracle

tests/libc/oracle/err_h.res.oracle

tests/libc/oracle/fc_libc.0.res.oracle

tests/libc/oracle/fc_libc.1.res.oracle

tests/libc/oracle/fc_libc.2.res.oracle