/usr/lib64/libxml2.so.2.9.7 in libxml2-2.9.7-2.fc28.x86_64 has not been linked with the standard Fedora linker flags (LDFLAGS) from redhat-rpm-config:

libtool: link: gcc -shared  -fPIC -DPIC  .libs/SAX.o .libs/entities.o .libs/encoding.o .libs/error.o .libs/parserInternals.o .libs/parser.o .libs/tree.o .libs/hash.o .libs/list.o .libs/xmlIO.o .libs/xmlmemory.o .libs/uri.o .libs/valid.o .libs/xlink.o .libs/HTMLparser.o .libs/HTMLtree.o .libs/debugXML.o .libs/xpath.o .libs/xpointer.o .libs/xinclude.o .libs/nanohttp.o .libs/nanoftp.o .libs/catalog.o .libs/globals.o .libs/threads.o .libs/c14n.o .libs/xmlstring.o .libs/buf.o .libs/xmlregexp.o .libs/xmlschemas.o .libs/xmlschemastypes.o .libs/xmlunicode.o .libs/xmlreader.o .libs/relaxng.o .libs/dict.o .libs/SAX2.o .libs/xmlwriter.o .libs/legacy.o .libs/chvalid.o .libs/pattern.o .libs/xmlsave.o .libs/xmlmodule.o .libs/schematron.o .libs/xzlib.o   -ldl -lz -llzma -lm  -O2 -g -fstack-protector-strong -grecord-gcc-switches -m64 -mtune=generic -mcet -Wl,--version-script=../libxml2.syms -Wl,-z -Wl,relro   -Wl,-soname -Wl,libxml2.so.2 -o .libs/libxml2.so.2.9.7

-specs=/usr/lib/rpm/redhat/redhat-hardened-ld is 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.