fix causes of some clippy warnings

[striezel]

Clippy linting had some errors:

error: boolean to int conversion using if
Error:   --> src/builders/module.rs:59:29
   |
59 |                 zend_debug: if PHP_DEBUG { 1 } else { 0 },
   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with from: `u8::from(PHP_DEBUG)`
   |
   = note: `-D clippy::bool-to-int-with-if` implied by `-D warnings`
   = note: `PHP_DEBUG as u8` or `PHP_DEBUG.into()` can also be valid options
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#bool_to_int_with_if

error: boolean to int conversion using if
Error:   --> src/builders/module.rs:60:22
   |
60 |                 zts: if PHP_ZTS { 1 } else { 0 },
   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with from: `u8::from(PHP_ZTS)`
   |
   = note: `PHP_ZTS as u8` or `PHP_ZTS.into()` can also be valid options
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#bool_to_int_with_if

error: could not compile `ext-php-rs` due to 2 previous errors

This PR tries to fix those.