This constant can be handy for tools like PIE to determine the origin of a PHP
binary to provide better output / diagnostics.
see php/pie#275
see php/php-src#18168
This information can be occasionally useful, and would otherwise need
to be parsed from `phpinfo()` output.
However, maybe more importantly we unify the build date between what is
given by `php -v` and `php -i`, since these compilation units are not
necessarily preprocessed within the same second.
Closes GH-16747.
The PHP_SBINDIR symbol was defined on *nix systems but never used. This
adds the constant similar to PHP_BINDIR also to PHP. On Windows it is
the value of prefix configuration when PHP was built (same value as
PHP_BINDIR).
Basically all constants are now declared via stubs. The rest of the constants are either deprecated (`SID` or `MHASH_*`) or out of interest (`__COMPILER_HALT_OFFSET__` and `PHP_CLI_PROCESS_TITLE`).
