hdf5_ep

[svn-r9662] Purpose:
Bug fix.

Description:
MIPSpro Compiler 7.4.x starts to support C99 features
but stdint.h has a "guard" in it that will #error if
cc is invoked without asking for C99 standard.  But it
does not result with a non-zero compiler exit code, thus
configure thought it is okay to use header file stdint.h.
This causes problems later.

Solution:
Default to use the C99 compiler if available.

Platforms tested:
Tested in Sandia tesla machine which is a new SGI machine.