mpfr: Update to version 4.2.0

mpfr: Update to version 4.2.0

- Update from version 4.1.1 to 4.2.0
- Update of rootfile
- Changelog
    Changes from versions 4.1.1 to version 4.2.0
	    Binary compatible with MPFR 4.0.* and 4.1.*, though some minor changes in
             the behavior of the formatted output functions may be visible, regarded as
             underspecified behavior or bug fixes (see below).
	    New functions mpfr_cosu, mpfr_sinu, mpfr_tanu, mpfr_acosu, mpfr_asinu,
             mpfr_atanu and mpfr_atan2u.
	    New functions mpfr_cospi, mpfr_sinpi, mpfr_tanpi, mpfr_acospi, mpfr_asinpi,
             mpfr_atanpi and mpfr_atan2pi.
	    New functions mpfr_log2p1, mpfr_log10p1, mpfr_exp2m1, mpfr_exp10m1 and
             mpfr_compound_si.
	    New functions mpfr_fmod_ui, mpfr_powr, mpfr_pown, mpfr_pow_uj, mpfr_pow_sj
             and mpfr_rootn_si (mpfr_pown is actually a macro defined as an alias for
             mpfr_pow_sj).
	    Bug fixes.
	        In particular, for the formatted output functions (mpfr_printf, etc.),
                 the case where the precision consists only of a period has been fixed
                 to be like .0 as specified in the ISO C standard, and the manual has
                 been corrected and clarified.
	        The macros of the custom interface have also been fixed: they now behave
                 like functions (except a minor limitation for mpfr_custom_init_set).

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Reviewed-by: Peter Müller <peter.mueller@ipfire.org>