Log Message:
mpfr: update to 4.0.1.

Changes from version 4.0.0 to version 4.0.1:
- Improved MPFR manual.
- Improved __GMP_CC and __GMP_CFLAGS retrieval (in particular for MS Windows).
- Fixed a build failure on some platforms when --with-gmp-build is used.
- Bug fixes (see ChangeLog file), in particular in mpfr_div_ui, which
  could yield an incorrectly rounded result to nearest when using
  different precisions; this bug had been present since the introduction
  of mpfr_div_ui, and in MPFR 4.0.0, it was affecting mpfr_div too.
- New: optional "make check-exported-symbols", mainly for the MPFR \ 
developers
  and binary distributions, to check that MPFR does not define symbols with a
  GMP reserved prefix (experimental).