DESC
Add some CFLAGS to Make.conf for more standards compatibility.
EDESC
Some systems/C libraries (dietlibc, for instance) also like having
_FILE_OFFSET_BITS=64 defined for large file access, and call "getconf
LFS_CFLAGS" to get the ones needed for access.

As including them doesn't hurt and should increase portability, the patch adds
them to CFLAGS in Make.conf.