fix a few warnings (format strings, unused variable)

During compilation gcc complains about the following:

perl.c:4970: warning: format '%u' expects argument of type 'unsigned int', but argument 2 has type 'U32' [-Wformat=]
perl.c:5075: warning: format '%u' expects argument of type 'unsigned int', but argument 2 has type 'I32' [-Wformat=]
mg.c:1972: warning: format '%ld' expects argument of type 'long int', but argument 2 has type 'ssize_t' [-Wformat=]
pp_ctl.c:2610: warning: unused variable 'mark' [-Wunused-variable]
regexec.c:2275: warning: format '%ld' expects argument of type 'long int', but argument 3 has type 'int' [-Wformat=]

This patch fixes all of them.

Tony: warning: unused variable 'mark' was fixed in 481c819b
update perldiag for the change in conversion specifiers
[perl #120043] fix some warnings

with an update for perldiag