CCFLAGS may have appendages not from PERL_MM_OPT.

At least on VMS, where the contents of DEFINE get added to it
because you have to have one /DEFINE qualifier containing all
the defines coming in from either CCFLAGS or DEFINE.

So test that what we got from PERL_MM_OPT is present in rather than
is exactly equivalent to what ends up in CCFLAGS.