which is more efficient on all targets.

In 84ba214c, I removed some redundant sign computations and in the
process, I incorrectly got rid of a temporary variable, thus passing
the absolute value of the input to bsloww1.  This caused #16623.

This fix undoes the incorrect change.

An incorrect variable name was used during the refactoring done in
commit 4aafb73c.

This patch consolidates the multiple copies of code that looks up sin
and cos of a number from the lookup table and computes the final
value, into static functions.  This does not have a noticeable
performance impact since the functions are inlined by gcc.

There is further scope for consolidation in the functions but they
cause a more noticable impact on performance (>5%) due to which I have
held back on them.

Removed more redundant computations in the slow paths of the sin and
cos functions.  The notable change is the passing of the most
significant bits of X to the slow functions to check if X is positive
so that just the absolute value of x can be passed and the repeated
ABS() operation is avoided.

The A and DA arguments in reduce_and_compute are useless and hence
have been removed.

There are multiple points in the code where the absolute value of a
number is computed multiple times or is computed even though the value
can only be positive.  This change removes those redundant
computations.  Tested on x86_64 to verify that there were no
regressions in the testsuite.

 - Remove redundant mynumber union definitions
 - Clean up a clumsy ternary operator
 - Rename TAYLOR_SINCOS to TAYLOR_SIN since we're only expanding the
   sin Taylor series in it.