tools/mpfr: update to 4.2.1

Changes from version 4.2.0 to version 4.2.1:
- Bug fixes (see <https://www.mpfr.org/mpfr-4.2.0/#fixed> and/or the
  ChangeLog file).
- Improved MPFR manual.
- Configure tests: replaced the test of the link with GMP, in order to
  avoid the use of a function without a prototype (Autoconf issue), as
  this is obsolescent in ISO C. The new test should be more robust.

Signed-off-by: Linhui Liu <liulinhui36@gmail.com>

tools/mpfr/Makefile

@@ -7,12 +7,12 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=mpfr
-PKG_VERSION:=4.2.0
+PKG_VERSION:=4.2.1
 PKG_CPE_ID:=cpe:/a:mpfr:gnu_mpfr
 
 PKG_SOURCE_URL:=@GNU/mpfr http://www.mpfr.org/mpfr-$(PKG_VERSION)
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
-PKG_HASH:=06a378df13501248c1b2db5aa977a2c8126ae849a9d9b7be2546fb4a9c26d993
+PKG_HASH:=277807353a6726978996945af13e52829e3abd7a9a5b7fb2793894e18f1fcbb2
 
 HOST_BUILD_PARALLEL:=1
 HOST_FIXUP:=autoreconf