Unused function in hssp-convert-3to1.cpp causes error in make on Mac OS 10.14.3

[mpavlak25]

Getting an unused function error on the make step of install on mac. Commenting out the function appears to resolve the issue.

/Library/Developer/CommandLineTools/usr/bin/make  all-am
depbase=`echo src/hssp-convert-3to1.o | sed 's|[^/]*$|.deps/&|;s|\.o$||'`;\
	g++ -DHAVE_CONFIG_H -I.  -std=c++11 -pedantic -Wall -Werror -Wno-reorder -pthread -I/usr/local/include -I./src/   -g -O2 -MT src/hssp-convert-3to1.o -MD -MP -MF $depbase.Tpo -c -o src/hssp-convert-3to1.o src/hssp-convert-3to1.cpp &&\
	mv -f $depbase.Tpo $depbase.Po
src/hssp-convert-3to1.cpp:588:8: error: unused function 'swap' [-Werror,-Wunused-function]
  void swap(seq& a, seq& b)
       ^
1 error generated.
make[1]: *** [src/hssp-convert-3to1.o] Error 1
make: *** [all] Error 2