Bug 6809

The POSIX.1 specification of tgamma says:

==
The value of x is a negative integer, or x is -Inf.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then
errno shall be set to [EDOM]. If the integer expression (math_errhandling &
MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be
raised.

==

For both -ve integer and -Inf, GNU's tgamma() correctly raises an FE_INVALID
exception.  However, errno is only correctly set (to EDOM) for the -ve integer
case.  For -Inf, errno is not set; it shoul dbe set to EDOM.

Background: 
On error, many glibc math functions both set errno and raise an exception
(fetestexcept(3)).  For example, the following  function all do this: acos(),
asin(), cosh(), sinh(), acosh(), asinh(), exp(), exp2(), ldexp(), log(),
log10(), log2().  However, there is much inconsistency.  Some functions raise an
exception, but don't set errno.  Some functions set errno for some errors, but
not others.  A few set errno, but don't raise an exception.  This series of bug
reports documents deviations from what I consider the ideal: all functions
should BOTH set errno AND raise an exception for all errors.

All of these reports relate to tests on glibc 2.8 (as provided by SUSE 11.0).