Check for lowercase 'bool' type at configuration stage. If not available
provide a suitable replacement with a type definition of 'unsigned char'
in setup_once.h
Move definitions of TRUE and FALSE to setup_once.h
making them available to any source code file which includes "setup.h".
Macro SOCKERRNO / SET_SOCKERRNO() returns / sets the *socket-related* errno
(or equivalent) on this platform to hide platform details to code using it.
Macro ERRNO / SET_ERRNO() returns / sets the NOT *socket-related* errno
(or equivalent) on this platform to hide platform details to code using it.
defining HAVE_SIGNAL_H if the header is available.
Added a check in configure that tests if the sig_atomic_t type is
available, defining HAVE_SIG_ATOMIC_T if it is available. Providing
a suitable default in setup_once.h if not available.
Added a check in configure that tests if the sig_atomic_t type is
already defined as volatile, defining HAVE_SIG_ATOMIC_T_VOLATILE
if it is available and already defined as volatile.