Constify to void build warning for C++ ext. [-Wwrite-strings]

Constify to void build warning for C++ ext. [-Wwrite-strings]

Example (with v8js):

/builddir/build/BUILD/php-pecl-v8js-1.3.4/NTS/v8js_class.cc: In function 'void v8js_execute_script(zval*, v8js_script*, long int, long int, long int, zval**)':
/usr/include/php/Zend/zend.h:204:57: warning: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]
 #define zend_bailout()  _zend_bailout(__FILE__, __LINE__)
                                                         ^
/builddir/build/BUILD/php-pecl-v8js-1.3.4/NTS/v8js_class.cc:633:3: note: in expansion of macro 'zend_bailout'
   zend_bailout();
   ^~~~~~~~~~~~