I am using MSys2/MinGW on Windows 7 to build an old project. MSys2 only uses the latest version of gcc and building the project with gcc v9.1.0 fails because it can't find an overloaded "<<" operator.
Through trial and error (and Cygwin), I have found that gcc v6.4.0 builds the project and v7.x does not.
Is there a CCFLAGS or CXXFLAGS option that I can use to make gcc v9.1.0 behave as if it was v6.4.0?