hdf5_msb

[svn-r24017] Bug fix: HDFFV-8500
The new gcc v4.8.* compilers does not work well with dt_arith which failed
in production mode.

Solution:
A temporary patch by removing any optimization (-O*) from the PROD_CFLAGS
so that dt_arith will pass for now.  A more through investigation is needed.

Tested: Jam and Koala where it failed and now passes.