Closes GH-5295.

Closes GH-5676.

Closes GH-4732.

If TSRM is shut down and started again (something that phpdbg does),
then tsrmls_id needs to be reloaded everywhere. As tsrmls_id
update is a rare operation, doing that shouldn't be a problem.

Normalization include:
- Use dnl for everything that can be ommitted when configure is built in
  favor of the shell comment character # which is visible in the output.
- Line length normalized to 80 columns
- Dots for most of the one line sentences
- Macro definitions include similar pattern header comments now

The `<signal.h>` header file is part of the standard C89 headers [1] and
on current systems can be included unconditionally.

Since file requires at least C89 or greater, the `HAVE_SIGNAL_H` symbol
defined by Autoconf in Zend.m4 [2] can be ommitted and simplifed.

The bundled libmagic (file) also ommits the usage of HAVE_SIGNAL_H since
5.35 however current version in PHP is very modified 5.34 version and
will be refactored separately. Check for HAVE_SIGNAL_H is therefore
still done in the configure.ac.

Refs:
[1] https://port70.net/~nsz/c/c89/c89-draft.html#4.1.2
[2] https://git.savannah.gnu.org/cgit/autoconf.git/tree/lib/autoconf/headers.m4