[appveyor-error] Fix MinGW32 build
[appveyor-error] Fix MinGW32 build

The Appveyor build for plain MinGW was not finding g++.exe; fix path

Tridify/oce,tpaviot/oce,tpaviot/oce,BenoitPerrot/oce,Tridify/oce,Tridify/oce,tpaviot/oce,tpaviot/oce,BenoitPerrot/oce,BenoitPerrot/oce,BenoitPerrot/oce,Tridify/oce,BenoitPerrot/oce,Tridify/oce,tpaviot/oce