build: Support declaring 32bit C functions that must reside in the f-segment

Add support for a FUNCFSEG macro that will force a "32bit flat" C
function to be located in the f-segment.  This is useful for 32bit
code with inline assembler that thunks to 16bit mode.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
2 files changed