Fix building in ISO C23

[ppisar]

Building with GCC 15, which defaults to ISO C23, failed like this:

In file included from lib/SDL_perl.xs:32:
lib/SDL_perl.c:654:13: error: conflicting types for ‘boot_SDL’; have ‘void(PerlInterpreter *, CV *)’ {aka ‘void(struct interpreter *, struct cv *)’}
  654 | XS_EXTERNAL(boot_SDL); /* prototype to pass -Wmissing-prototypes */
  |             ^~~~~~~~
/usr/lib64/perl5/CORE/XSUB.h:149:34: note: in definition of macro ‘XS_EXTERNAL’
  149 | #  define XS_EXTERNAL(name) void name(pTHX_ CV* cv __attribute__unused__)
  |                                  ^~~~
lib/SDL_perl.xs:147:6: note: previous declaration of ‘boot_SDL’ with type ‘void(void)’
  147 | void boot_SDL();
  |      ^~~~~~~~
lib/SDL_perl.c:655:13: error: conflicting types for ‘boot_SDL’; have ‘void(PerlInterpreter *, CV *)’ {aka ‘void(struct interpreter *, struct cv *)’}
  655 | XS_EXTERNAL(boot_SDL)
  |             ^~~~~~~~
/usr/lib64/perl5/CORE/XSUB.h:149:34: note: in definition of macro ‘XS_EXTERNAL’
  149 | #  define XS_EXTERNAL(name) void name(pTHX_ CV* cv __attribute__unused__)
  |                                  ^~~~
lib/SDL_perl.xs:147:6: note: previous declaration of ‘boot_SDL’ with type ‘void(void)’
  147 | void boot_SDL();
  |      ^~~~~~~~

The cause is a mismatch between how boot_SDL() was declared and used in src/SDL.xs and how Perl generates a boot function for XS packages. This patch fixes it by passing current Perl interpreter and, probably ignored, cv argument.

Resolves: #294
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2341036