The type `short float` is proposed for the C language in ISO/IEC JTC
1/SC 22 WG 14 (C WG) for mainly IEEE 754-2008 binary16, a.k.a.
half-precision floating point or FP16.
By this commit, `short float` and `short float _Complex` are detected
in `configure` and used in Open MPI internal code. `MPI_SHORT_FLOAT`
and its complex number version are not added yet.
This commit changes values of existing `OPAL_DATATYPE_*` macros.
This change does not affect ABI compatibility of `libmpi.so` and the
like because these values are only used in OPAL and OMPI internal code.
Signed-off-by: KAWASHIMA Takahiro <t-kawashima@jp.fujitsu.com>