Relax the compat CFLAGS a bit

While some of it still applies, the rest was devised for an older target device,
and with a different TC.
This was checked w/ Linaro binary TCs from Ubuntu. We should now run on
anything running at least (e)glibc 2.7.
Minor cosmetic tweaks in comments
More comments tweak
Move some comments around
Merge pull request #208 from NiLuJe/master

Relax the compat CFLAGS