SCons: Treat all warnings as errors
SCons: Treat all warnings as errors

After an effort spanning several years, we should now be warning-free
on all major compilers, so we can set `-Werror` to ensure that we don't
introduce warnings in new code.

Disable -Werror=strict-overflow on GCC 7 though, as it seems bogus and
was fixed in 8+.

vnen/godot,vnen/godot,Faless/godot,Faless/godot,honix/godot,josempans/godot,vnen/godot,Valentactive/godot,vnen/godot,vkbsb/godot,guilhermefelipecgs/godot,Paulloz/godot,MarianoGnu/godot,pkowal1982/godot,vkbsb/godot,MarianoGnu/godot,vkbsb/godot,akien-mga/godot,firefly2442/godot,ZuBsPaCe/godot,godotengine/godot,josempans/godot,DmitriySalnikov/godot,BastiaanOlij/godot,Paulloz/godot,ZuBsPaCe/godot,akien-mga/godot,Faless/godot,Shockblast/godot,Faless/godot,vkbsb/godot,guilhermefelipecgs/godot,akien-mga/godot,sanikoyes/godot,Valentactive/godot,sanikoyes/godot,guilhermefelipecgs/godot,akien-mga/godot,Faless/godot,josempans/godot,ZuBsPaCe/godot,firefly2442/godot,pkowal1982/godot,Shockblast/godot,MarianoGnu/godot,pkowal1982/godot,honix/godot,pkowal1982/godot,MarianoGnu/godot,ZuBsPaCe/godot,josempans/godot,godotengine/godot,ZuBsPaCe/godot,Zylann/godot,firefly2442/godot,Faless/godot,Valentactive/godot,Paulloz/godot,Faless/godot,sanikoyes/godot,akien-mga/godot,Zylann/godot,Shockblast/godot,BastiaanOlij/godot,josempans/godot,firefly2442/godot,honix/godot,honix/godot,BastiaanOlij/godot,BastiaanOlij/godot,Valentactive/godot,Paulloz/godot,vkbsb/godot,Valentactive/godot,Paulloz/godot,sanikoyes/godot,DmitriySalnikov/godot,DmitriySalnikov/godot,MarianoGnu/godot,BastiaanOlij/godot,Faless/godot,Valentactive/godot,godotengine/godot,BastiaanOlij/godot,godotengine/godot,guilhermefelipecgs/godot,vnen/godot,godotengine/godot,sanikoyes/godot,pkowal1982/godot,firefly2442/godot,pkowal1982/godot,Zylann/godot,honix/godot,Zylann/godot,guilhermefelipecgs/godot,Shockblast/godot,Shockblast/godot,MarianoGnu/godot,DmitriySalnikov/godot,BastiaanOlij/godot,sanikoyes/godot,sanikoyes/godot,guilhermefelipecgs/godot,ZuBsPaCe/godot,Valentactive/godot,Shockblast/godot,guilhermefelipecgs/godot,godotengine/godot,firefly2442/godot,MarianoGnu/godot,akien-mga/godot,ZuBsPaCe/godot,vnen/godot,Zylann/godot,DmitriySalnikov/godot,vkbsb/godot,godotengine/godot,josempans/godot,Paulloz/godot,firefly2442/godot,honix/godot,josempans/godot,akien-mga/godot,Zylann/godot,godotengine/godot,guilhermefelipecgs/godot,Shockblast/godot,Zylann/godot,BastiaanOlij/godot,pkowal1982/godot,sanikoyes/godot,MarianoGnu/godot,Zylann/godot,Paulloz/godot,Shockblast/godot,firefly2442/godot,pkowal1982/godot,josempans/godot,vkbsb/godot,ZuBsPaCe/godot,DmitriySalnikov/godot,vkbsb/godot,Valentactive/godot,vnen/godot,DmitriySalnikov/godot,vnen/godot,akien-mga/godot