tools/mpc: update to 1.3.1

tools/mpc: update to 1.3.1

Version 1.3.1 new features:
	Bug fix: It is again possible to include mpc.h without including stdio.h.
Version 1.3.0 new features:
    New function: mpc_agm
    New rounding modes "away from zero", indicated by the letter "A" and corresponding to MPFR_RNDA on the designated real or imaginary part.
    New experimental ball arithmetic.
    New experimental function: mpc_eta_fund
    Bug fixes:
        mpc_asin for asin(z) with small |Re(z)| and tiny |Im(z)|
        mpc_pow_fr: sign of zero part of result when the base has up to sign the same real and imaginary part, and the exponent is an even positive integer
        mpc_fma: the returned int value was incorrect in some cases (indicating whether the rounded real/imaginary parts were smaller/equal/greater than the exact values), but the computed complex value was correct.
    Remove the unmaintained Makefile.vc; build files for Visual Studio are maintained independently by Brian Gladman.

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