[perl #39313] [TODO] or [BUG] improve PMC compiler

[via RT]

# New Ticket Created by  Leopold Toetsch 
# Please include the string:  [perl #39313]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/rt3/Ticket/Display.html?id=39313 >


It's easy to add 'invalide' code to .pmc files. E.g. I had defined:

    METHOD parent() {
        return PMC_pmc_val(SELF) ? PMC_pmc_val(SELF) : PMCNULL;
    }

Due to the absence of a return value, the PMC compiler just ignores this 
'method' without further notice.

This also is happening, if there's just a whitespace before the '*':

    METHOD PMC *parent() {
        return PMC_pmc_val(SELF) ? PMC_pmc_val(SELF) : PMCNULL;
    }

This totally valid C type declaration is just ignored.

Fixes welcome,
leo