/usr/lib64/libhdf5.so.10.3.1 and other objects in in hdf5-1.8.20-2.fc28.x86_64 are not linked with the default Fedora linker flags (LDFLAGS) from redhat-rpm-config:

libtool: link: gcc -shared  -fPIC -DPIC  .libs/H5.o .libs/H5checksum.o .libs/H5dbg.o .libs/H5system.o .libs/H5timer.o .libs/H5trace.o .libs/H5A.o .libs/H5Abtree2.o .libs/H5Adense.o .libs/H5Adeprec.o .libs/H5Aint.o .libs/H5Atest.o .libs/H5AC.o .libs/H5B.o .libs/H5Bcache.o .libs/H5Bdbg.o .libs/H5B2.o .libs/H5B2cache.o .libs/H5B2dbg.o .libs/H5B2hdr.o .libs/H5B2int.o .libs/H5B2stat.o .libs/H5B2test.o .libs/H5C.o .libs/H5CS.o .libs/H5D.o .libs/H5Dbtree.o .libs/H5Dchunk.o .libs/H5Dcompact.o .libs/H5Dcontig.o .libs/H5Ddbg.o .libs/H5Ddeprec.o .libs/H5Defl.o .libs/H5Dfill.o .libs/H5Dint.o .libs/H5Dio.o .libs/H5Dlayout.o .libs/H5Dmpio.o .libs/H5Doh.o .libs/H5Dscatgath.o .libs/H5Dselect.o .libs/H5Dtest.o .libs/H5E.o .libs/H5Edeprec.o .libs/H5Eint.o .libs/H5F.o .libs/H5Fint.o .libs/H5Faccum.o .libs/H5Fcwfs.o .libs/H5Fdbg.o .libs/H5Fefc.o .libs/H5Ffake.o .libs/H5Fio.o .libs/H5Fmount.o .libs/H5Fmpi.o .libs/H5Fquery.o .libs/H5Fsfile.o .libs/H5Fsuper.o .libs/H5Fsuper_cache.o .libs/H5Ftest.o .libs/H5FD.o .libs/H5FDcore.o .libs/H5FDdirect.o .libs/H5FDfamily.o .libs/H5FDint.o .libs/H5FDlog.o .libs/H5FDmpi.o .libs/H5FDmpio.o .libs/H5FDmulti.o .libs/H5FDsec2.o .libs/H5FDspace.o .libs/H5FDstdio.o .libs/H5FL.o .libs/H5FO.o .libs/H5FS.o .libs/H5FScache.o .libs/H5FSdbg.o .libs/H5FSsection.o .libs/H5FSstat.o .libs/H5FStest.o .libs/H5G.o .libs/H5Gbtree2.o .libs/H5Gcache.o .libs/H5Gcompact.o .libs/H5Gdense.o .libs/H5Gdeprec.o .libs/H5Gent.o .libs/H5Gint.o .libs/H5Glink.o .libs/H5Gloc.o .libs/H5Gname.o .libs/H5Gnode.o .libs/H5Gobj.o .libs/H5Goh.o .libs/H5Groot.o .libs/H5Gstab.o .libs/H5Gtest.o .libs/H5Gtraverse.o .libs/H5HF.o .libs/H5HFbtree2.o .libs/H5HFcache.o .libs/H5HFdbg.o .libs/H5HFdblock.o .libs/H5HFdtable.o .libs/H5HFhdr.o .libs/H5HFhuge.o .libs/H5HFiblock.o .libs/H5HFiter.o .libs/H5HFman.o .libs/H5HFsection.o .libs/H5HFspace.o .libs/H5HFstat.o .libs/H5HFtest.o .libs/H5HFtiny.o .libs/H5HG.o .libs/H5HGcache.o .libs/H5HGdbg.o .libs/H5HGquery.o .libs/H5HL.o .libs/H5HLcache.o .libs/H5HLdbg.o .libs/H5HLint.o .libs/H5HP.o .libs/H5I.o .libs/H5Itest.o .libs/H5L.o .libs/H5Lexternal.o .libs/H5lib_settings.o .libs/H5MF.o .libs/H5MFaggr.o .libs/H5MFdbg.o .libs/H5MFsection.o .libs/H5MM.o .libs/H5MP.o .libs/H5MPtest.o .libs/H5O.o .libs/H5Oainfo.o .libs/H5Oalloc.o .libs/H5Oattr.o .libs/H5Oattribute.o .libs/H5Obogus.o .libs/H5Obtreek.o .libs/H5Ocache.o .libs/H5Ochunk.o .libs/H5Ocont.o .libs/H5Ocopy.o .libs/H5Odbg.o .libs/H5Odrvinfo.o .libs/H5Odtype.o .libs/H5Oefl.o .libs/H5Ofill.o .libs/H5Oginfo.o .libs/H5Olayout.o .libs/H5Olinfo.o .libs/H5Olink.o .libs/H5Omessage.o .libs/H5Omtime.o .libs/H5Oname.o .libs/H5Onull.o .libs/H5Opline.o .libs/H5Orefcount.o .libs/H5Osdspace.o .libs/H5Oshared.o .libs/H5Ostab.o .libs/H5Oshmesg.o .libs/H5Otest.o .libs/H5Ounknown.o .libs/H5P.o .libs/H5Pacpl.o .libs/H5Pdapl.o .libs/H5Pdcpl.o .libs/H5Pdeprec.o .libs/H5Pdxpl.o .libs/H5Pfapl.o .libs/H5Pfcpl.o .libs/H5Pfmpl.o .libs/H5Pgcpl.o .libs/H5Pint.o .libs/H5Plapl.o .libs/H5Plcpl.o .libs/H5Pocpl.o .libs/H5Pocpypl.o .libs/H5Pstrcpl.o .libs/H5Ptest.o .libs/H5PL.o .libs/H5R.o .libs/H5Rdeprec.o .libs/H5RC.o .libs/H5RS.o .libs/H5S.o .libs/H5Sall.o .libs/H5Sdbg.o .libs/H5Shyper.o .libs/H5Smpio.o .libs/H5Snone.o .libs/H5Spoint.o .libs/H5Sselect.o .libs/H5Stest.o .libs/H5SL.o .libs/H5SM.o .libs/H5SMbtree2.o .libs/H5SMcache.o .libs/H5SMmessage.o .libs/H5SMtest.o .libs/H5ST.o .libs/H5T.o .libs/H5Tarray.o .libs/H5Tbit.o .libs/H5Tcommit.o .libs/H5Tcompound.o .libs/H5Tconv.o .libs/H5Tcset.o .libs/H5Tdbg.o .libs/H5Tdeprec.o .libs/H5Tenum.o .libs/H5Tfields.o .libs/H5Tfixed.o .libs/H5Tfloat.o .libs/H5Tinit.o .libs/H5Tnative.o .libs/H5Toffset.o .libs/H5Toh.o .libs/H5Topaque.o .libs/H5Torder.o .libs/H5Tpad.o .libs/H5Tprecis.o .libs/H5Tstrpad.o .libs/H5Tvisit.o .libs/H5Tvlen.o .libs/H5TS.o .libs/H5VM.o .libs/H5WB.o .libs/H5Z.o .libs/H5Zdeflate.o .libs/H5Zfletcher32.o .libs/H5Znbit.o .libs/H5Zshuffle.o .libs/H5Zszip.o .libs/H5Zscaleoffset.o .libs/H5Ztrans.o   -lsz -lz -ldl -lm  -O -O2 -g -fstack-protector-strong -grecord-gcc-switches -m64 -mtune=generic -mcet -Wl,-z -Wl,relro   -Wl,-soname -Wl,libhdf5.so.10 -o .libs/libhdf5.so.10.3.1

It seems that the -specs=/usr/lib/rpm/redhat/redhat-hardened-ld flag has gone missing.

See https://src.fedoraproject.org/rpms/redhat-rpm-config/blob/master/f/buildflags.md for information on RPM macros and environment variables provided by the build environment.