build errors with save-git.c and upstream libgit2

[Lutz Vieweg]

Hi,

I seem to need "-DUSE_LIBGIT21_API=1" to make subsurface with
the current libgit2 sources.

What is the recommended way to enable that for building?

I found in subsurface-configure.pri:
> libgit21-api {
> 	DEFINES += USE_LIBGIT21_API
> }
... but I don't know what/when would use that .pri file.

(For now I've patched my Makefile, manually, which is probably
not the recommended method, I suppose.)

Regards,

Lutz Vieweg