Dear all,

the compile-time simplification of intrinsic SET_EXPONENT was
broken since the early days of gfortran for argument X < 1
(including negative X) and for I < 0.  I identified and fixed
several issues in the implementation.  The testcase explores
argument space comparing compile-time and runtime results and
is checked against Intel.

Regtested on x86_64-pc-linux-gnu.  OK for mainline?

This is not a regression, but can lead to wrong code.
Would it be OK to backport to open branches?

Thanks,
Harald