Fixed mutex problem on MinGW32.
Fixed mutex problem on MinGW32.

jpflori/flint2,wbhart/flint2,wbhart/flint2,dsroche/flint2,dsroche/flint2,fredrik-johansson/flint2,fredrik-johansson/flint2,wbhart/flint2,jpflori/flint2,fredrik-johansson/flint2,jpflori/flint2,dsroche/flint2,dsroche/flint2,jpflori/flint2