mpfr: update to 4.1.0.

Changes from versions 4.0.* to version 4.1.0:
- The "épinards à la crème" release.
- Binary compatible with MPFR 4.0.*, 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 --enable-formally-proven-code configure option, to use (when available)
  formally proven code.
- Improved __GMP_CC and __GMP_CFLAGS retrieval (in particular for MS Windows).
- Option -pedantic is now always removed from __GMP_CFLAGS (see INSTALL).
- Changed __float128 to the type _Float128 specified in ISO/IEC TS 18661.
  __float128 is used as a fallback if _Float128 is not supported.
- New function mpfr_get_str_ndigits about conversion to a string of digits.
- New function mpfr_dot for the dot product (incomplete, experimental).
- New functions mpfr_get_decimal128 and mpfr_set_decimal128 (available only
  when MPFR has been built with decimal float support).
- New function mpfr_cmpabs_ui.
- New function mpfr_total_order_p for the IEEE 754 totalOrder predicate.
- The mpfr_out_str function now accepts bases from -2 to -36, in order to
  follow mpfr_get_str and GMP's mpf_out_str functions (these cases gave an
  assertion failure, as with other invalid bases).
- Shared caches: cleanup; really detect lock failures (abort in this case).
- The behavior of the formatted output functions (mpfr_printf, etc.) with
  an empty precision field has improved: trailing zeros are kept in a way
  similar to the formatted output functions from C.
- Improved mpfr_add and mpfr_sub when all operands have a precision equal to
  twice the number of bits per word, e.g., 128 bits on a 64-bit platform.
- Optimized the tuning parameters for various architectures.
- Improved test coverage to 98.6% of code for x86_64.
- Bug fixes.
- MPFR manual: corrected/completed the mpfr_get_str description in order to
  follow the historical behavior and GMP's mpf_get_str function.
- 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).
- Mini-gmp support: replaced --enable-mini-gmp configure option by
  --with-mini-gmp (still experimental, read doc/mini-gmp).
- A GCC bug on Sparc (present at least in old GCC 4.5.3 and 5.5.0 versions),
  which made several tests fail when TLS was enabled, is now avoided in the
  tests. The MPFR library itself was not affected and normal code using the
  MPFR library should not be affected either. Users and distributions that
  disabled TLS just because of the test failures can safely re-enable it.


(wiz)