Fix for Coverity perl5 CID 29034: Out-of-bounds read (OVERRUN) overrun-local: Overrun...

Fix for Coverity perl5 CID 29034: Out-of-bounds read (OVERRUN) overrun-local: Overrunning array PL_reg_intflags name of 14 8-byte elements at element index 31 (byte offset 248) using index bit (which evaluates to 31).

Needed compile-time limits for the PL_reg_intflags_name so that the
bit loop doesn't waltz off past the array.  Could not use C_ARRAY_LENGTH
because the size of name array is not visible during compile time
(only const char*[] is), so modified regcomp.pl to generate the size,
made it visible only under DEBUGGING.  Did extflags analogously
even though its size currently exactly 32 already.  The sizeof(flags)*8
is extra paranoia for ILP64.