RE: libm -fno-builtin

Hi,

Yes -fno-builtin should not be used indeed as it disables lots of useful optimizations.
Removing -fno-builtin should have no negative effects except for eg. memcpy where
compilers can recognize an overly simplistic implementation and optimize it to a 
call to memcpy... I think you will need a -fno-builtin-memcpy when building the size
optimized version of libc/string/memcpy.c given it is marked with restrict.

I think a config option is overkill.

Wilco