Fix php_module_startup() when loading more than one additional module

Dereferencing addition_modules within php_module_startup would
point to a vector entirely on the stack (which is of course, wrong).

Use a specialized helper to keep BC with the current php_module_startup()
calling semantics.

Fixes 63159
Thanks to @a-j-k
Merge branch 'PHP-5.5' into PHP-5.6

* PHP-5.5:
  Fix php_module_startup() when loading more than one additional module
Merge branch 'PHP-5.6'

* PHP-5.6:
  Fix php_module_startup() when loading more than one additional module