On the return type of main:
If we're using a version of gcc that has my "official" patches, which
I submitted for 2.7.2.2 or so, you can suppress this with -Wno-main,
or with -ffreestanding.  The latter implies -fno-builtin, also.

If we're using one of my prior patch sets, I think you just have to ignore
the warning; I had not been thinking of freestanding environments.

-s