[PATCH 0/5] errno changes for libm

Here's a series which reflects the review I did about newlib errno in
various math functions.

Patches 1-3 change the errno value used in gamma and y functions to
match the POSIX spec which uses ERANGE in several places that used to
set EDOM.

Patches 1-3 and patch 4 change POSIX math functions so that they don't
adjust values returned from the IEEE functions; none of those
adjustments were necessary, and some of them were incorrect when
compared with POSIX. This way, enabling errno support in the library
doesn't also change what the functions return.

Patch 5 is a proposed method for making newlib errno reporting
consistent between all math functions. It uses _IEEE_LIBM across the
whole library to select whether errno is set at library build
time. When _IEEE_LIBM is not set, errno is always set by math
functions when required. When _IEEE_LIBM is set, errno is never
modified by math functions.