This avoids bringing in additional code when using error functions
without --gc-sections.

Two functions from each file are now global and have been renamed to start with __math:

	with_errno → __math_with_errno
	with_errnof → __math_with_errnof
	xflow → __math_xflow
	xflowf → __math_xflowf

There should be no functional changes to the resulting code.
Signed-off-by: Keith Packard <keithp@keithp.com>