[3.0] contrib: update mingw-w64 to v10

This is the latest stable release. We can update our Docker images as well.

We can now detect the proper dcomp.h with the installed mingw-w64 version. See 50e71ad6

(cherry picked from commit e3e0854b) (edited) edited:

• 3.0 doesn't need the dcomp target
• 3.0 did not have a SHA512SUMS yet
• 3.0 was using check_githash for the git version