CAST_INLINE - is it ever defined? Was it ever defined?

[richardleach]

Description
3bb7c1b added inline macros for I_32, U_32, I_V, U_V as an alternative to the pre-existing macros that call the relevant Perl_cast_* function. These inline macros are guarded by CAST_INLINE (https://github.com/Perl/perl5/blob/blead/perl.h#L4795).

However:

• The commit didn't add anything like a Configure check that would set CAST_INLINE.
• Today's Configure doesn't contain that string, nor do any of the hint files.

Is this dead code? If so, should Configure start setting CAST_INLINE - and under what conditions - or should it be ripped out?

Steps to Reproduce
perl -V or grep -r CAST_INLINE * on a git clone of blead.

Expected behavior
CAST_INLINE is either defined somewhere by something, or it is removed and only one set of cast macros remains.

Perl configuration

Characteristics of this binary (from libperl): 
  Compile-time options:
    HAS_LONG_DOUBLE
    HAS_STRTOLD
    HAS_TIMES
    MULTIPLICITY
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_HASH_FUNC_SIPHASH13
    PERL_HASH_USE_SBOX32
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_USE_DEVEL
    PERL_USE_SAFE_PUTENV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_ITHREADS
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
    USE_REENTRANT_API
    USE_THREAD_SAFE_LOCALE