Fix ifort warning flag.
Restore AC_DEFUN([PAC_PROG_FC_DEFAULT_REALisDBLE] in m4/aclocal_fc.m4.
Add --enable-symbols, --enable-profiling, and --enable-optimization
options to autotools configure; all configure flags for
--enable-production and --disable-production should match HDF5 1.10 and
1.12 production and debug default flags.
