libmpc: Update to 1.2.1

libmpc: Update to 1.2.1

- Update from 1.1.0 to 1.2.1
- Update of rootfiles
- Changelog
   Version 1.2.1, "Hyacinthus orientalis", released in October 2020, comes with the following new features:
    Bug fixes:
        Fix an incompatibility problem with GMP 6.0 and before.
        Fix an intermediate overflow in asin.
   Version 1.2.0, "Hyacinthus orientalis", released in August 2020, comes with the following new features:
    Minimally required library version: mpfr 4.1.0
    New functions:
        mpc_sum
        mpc_dot
    Several functions are more robust with a reduced exponent range (for example corresponding to IEEE 754 binary formats).
    New mpcheck tool for comparison with the native C library

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>