phpize: fix silently stale build files when the PHP install is read-only

[GromNaN]

phpize_copy_files() copies build/* and run-tests.php from the PHP installation into the extension directory using plain cp.

Homebrew installs those files read-only, mode 444 and 555. On the first phpize run the destination is created with the source's mode, so it is read-only too. On every subsequent run in the same extension directory, cp cannot open the destination for writing and fails with "Permission denied". Any installation that makes these files read-only will hit the same thing.

The failure is not detected. Both cp calls run in subshells whose exit status is discarded, phpize_copy_files is called unconditionally, and phpize exits 0. So phpize reports success while leaving the previous run's files in place.

That is the real hazard. The visible error lines are only a symptom; the consequence is that the extension is then configured and built against stale php.m4, Makefile.global and run-tests.php. After upgrading PHP in place, an extension can be configured with the previous PHP's build system without any signal that something went wrong.

Two changes, split so they can be judged separately:

1. Use cp -f. It unlinks and recreates the destination, so it needs write permission on the directory only, not on the target file. This alone fixes the failure. -f is POSIX.
2. Append || exit 1 to both subshells so a copy failure aborts phpize instead of continuing with stale files. This matches the style already used by phpize_autotools() just below.

Verified on macOS with Homebrew PHP 8.5.10: the substituted script still passes sh -n, and cp fails while cp -f succeeds against a mode 444 destination.