perf scripting perl: Ignore some warnings to keep building with perl headers

perf scripting perl: Ignore some warnings to keep building with perl headers

On gcc 12 we started seeing this:

  In file included from /usr/lib/perl5/5.36.0/x86_64-linux-thread-multi/CORE/perl.h:2999,
                   from util/scripting-engines/trace-event-perl.c:35:
  /usr/lib/perl5/5.36.0/x86_64-linux-thread-multi/CORE/inline.h: In function 'Perl_is_utf8_valid_partial_char_flags':
  /usr/lib/perl5/5.36.0/x86_64-linux-thread-multi/CORE/handy.h:125:23: error: cast from function call of type 'STRLEN' {aka 'long unsigned int'} to non-matching type '_Bool' [-Werror=bad-function-cast]
    125 | #define cBOOL(cbool) ((bool) (cbool))
        |                       ^
  /usr/lib/perl5/5.36.0/x86_64-linux-thread-multi/CORE/inline.h:2363:12: note: in expansion of macro 'cBOOL'
   2363 |     return cBOOL(is_utf8_char_helper_(s0, e, flags));
        |            ^~~~~
  In file included from /usr/lib/perl5/5.36.0/x86_64-linux-thread-multi/CORE/perl.h:7242:
  /usr/lib/perl5/5.36.0/x86_64-linux-thread-multi/CORE/inline.h: In function 'Perl_cop_file_avn':
  /usr/lib/perl5/5.36.0/x86_64-linux-thread-multi/CORE/inline.h:3489:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
   3489 |     const char *file = CopFILE(cop);
        |     ^~~~~
  In file included from /usr/lib/perl5/5.36.0/x86_64-linux-thread-multi/CORE/perl.h:7243:
  /usr/lib/perl5/5.36.0/x86_64-linux-thread-multi/CORE/sv_inline.h: In function 'Perl_newSV_type':
  /usr/lib/perl5/5.36.0/x86_64-linux-thread-multi/CORE/sv_inline.h:376:5: error: enumeration value 'SVt_LAST' not handled in switch [-Werror=switch-enum]
    376 |     switch (type) {
        |     ^~~~~~

So disable those warnings to keep building with perl devel headers.

Noticed, among other distros, on opensuse tumbleweed:

gcc version 12.1.1 20220629 [revision 7811663964aa7e31c3939b859bbfa2e16919639f] (SUSE Linux)

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>