[PATCH] Fortran: make IEEE_VALUE produce signaling NaNs

[FX]

Hi Mikael, team,

> Thanks. Pushed: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=90045c5df5b3c8853e7740fb72a11aead1c489bb

Pushed a further commit to XFAIL the testcases on x87:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=86e3b476d5defaa79c94d40b76cbeec21cd02e5f

There the ABI does not allow us to meaningfully pass signaling NaNs in float and double types, sadly.

FX