mpc: Fix mingw build
mpc: Fix mingw build

Cannot build both static and shared version for mingw, as gmp is required,
and that cannot be build both shared and static for mingw.

Signed-off-by: Esben Haabendal <c5ba3f1141bb30a64dd6c7e6726a53a85adc9442@prevas.dk>

diorcety/oe-lite-core,hundeboll/core,sknsean/core,hundeboll/core,sknsean/core,hundeboll/core,sknsean/core,diorcety/oe-lite-core,sknsean/core,hundeboll/core,sknsean/core