Automatically build Math::MPFR with __float128 support if mpfr_buildopt_float128_p() returns true && 'F128=0' has not been provided as an argument to Makefile.PL.
Automatically build Math::MPFR with _Decimal64 support if mpfr_buildopt_decimal_p() returns true && 'D64=0' has not been provided as an argument to Makefile.PL.
Make sure that _Float128 is a known type when MPFR_WANT_FLOAT128 is defined (because it appears in mpfr.h in mpfr-4.1.0).
Add '-lquadmath' to LIBS in Makefile.PL (as some Cygwin builds apparently want it).
Prototype those subs specified in 'use subs'.
Alter Prec.xs, Random.xs and V.xs to accommodate perl.h's defining (as of 5.28.7) of INTMAX_C and UINTMAX_C. (Replaced '#include <mpfr.h>' with '#include "../math_mpfr_include.h"