jerry13/ccache — comment on commit e3a53886865cc8c5e5e37a31b1ab2985ee197a23
File: ccache.c line 973
By jrosdahl:

But why does Visual Studio care how ccache names files in the cache? The name is a ccache implementation detail.

Sure, the .o prefix for object files in the cache was chosen because object files in Unix environments typically have this extension, but it has nothing to do with what they are called in the build directory. (Actually, the object files had no extension at all in the cache in ccache 2.4.)