hdf5_ep

[svn-r10171] Purpose:
Bug fix

Description:
The fortran compiler is named FC.  If F9X environment variable is set,
FC should hold the value in F9X.  However, this was overwriting values
written to FC by platform-specific config scripts.
This caused copper to find the wrong fortran when building in parallel, and
may have had other symptoms on other platforms.

Solution:
Assign $F9X to $FC at the beginning of configure, before platform-specific
scripts are run.  Do this assignment only if FC is empty.

Platforms tested:
copper, modi4 (parallel and serial w/c++), verbena.
This change should only affect fortran build.