rename and function-ise dtrace macros

rename and function-ise dtrace macros

This commit:

1. Renames the various dtrace probe macros into a consistent and
self-documenting pattern, e.g.

ENTRY_PROBE  => PERL_DTRACE_PROBE_ENTRY
RETURN_PROBE => PERL_DTRACE_PROBE_RETURN

Since they're supposed to be defined only under PERL_CORE, this shouldn't
break anything that's not being naughty.

2. Implement the main body of these macros using a real function.

They were formerly defined along the lines of

    if (PERL_SUB_ENTRY_ENABLED())
        PERL_SUB_ENTRY(...);

The PERL_SUB_ENTRY() part is a macro generated by the dtrace system, which
for example on linux expands to a large bunch of assembly directives.
Replace the direct macro with a function wrapper, e.g.

    if (PERL_SUB_ENTRY_ENABLED())
        Perl_dtrace_probe_call(aTHX_ cv, TRUE);

This reduces to once the number of times the macro is expanded.

The new functions also take simpler args and then process the values they
need using intermediate temporary vars to avoid huge macro expansions.

For example

    ENTRY_PROBE(CvNAMED(cv)
                    ? HEK_KEY(CvNAME_HEK(cv))
                    : GvENAME(CvGV(cv)),
                CopFILE((const COP *)CvSTART(cv)),
                CopLINE((const COP *)CvSTART(cv)),
                CopSTASHPV((const COP *)CvSTART(cv)));

is now

    PERL_DTRACE_PROBE_ENTRY(cv);

This reduces the executable size by 1K on -O2 -Dusedtrace builds,
and by 45K on -DDEBUGGING -Dusedtrace builds.