undefine pagesize

add undef PAGESIZE to clear redefinition warning on platforms
where this value is already set, maintaining current behavior of
retrieving this value from POSIX defined sysconf(_SC_PAGESIZE).
fix incorrect include redirects

changes include headers sys/errno to errno
sys/signal to signal and wait to sys/wait
replace __va_list with va_list

most of the codebase already uses va_list, which is specified by
iso-c. gcc/glibc provides 'typedef __gnuc_va_list va_list'. and
when not using gcc/glibc we can't expect to find __gnuc_va_list.