[libm] Fix undefined behavior of a left shifted of a signed integerHEADmain

The patch fixes a few instances of left shifts on
signed integer entities.  A 'static inline' helper function
'subnormal_ilogb()' has been added to math_private.h.  This
function is then used e_fmod.c, s_ilogb(), and s_remquo.c.

The change in s_remquo.c has only been compile tested.

The change to e_fmod.c has been test on over 3 billion pairs
of subnormal numbers where testing included x > y and x < y
pairs.  The test compared the output from fmod() with the
output from mpfr_fmod() from MPFR.  There were no difference.

The change to s_ilogb() has had limited testing where its
output was compared against frexp().  In this testing, no
differences in output were detected.

PR:	288778
MFC after:	1 week

0 files changed, 0 insertions, 0 deletions