zig cc: default to a.exe on windows
zig cc: default to a.exe on windows

This matches Clang. Thanks to Abner Coimbre for pointing this out.

raulgrell/zig,raulgrell/zig,zig-lang/zig,zig-lang/zig,andrewrk/zig,raulgrell/zig,andrewrk/zig,zig-lang/zig,raulgrell/zig,raulgrell/zig