FTBFS with GCC 6: no matching function for call to

libtool: compile: g++ -DHAVE_CONFIG_H -I. -I.. -I../ -DPACKAGE_DATA_DIR=\"/usr/share\" -DPACKAGE_LOCALE_DIR=\"/usr/share/locale\" -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/libxml2 -Wdate-time -D_FORTIFY_SOURCE=2 -g -O2 -fdebug-prefix-map=/«PKGBUILDDIR»=. -fstack-protector-strong -Wformat -Werror=format-security -c Number.cc -o Number.o >/dev/null 2>&1
/bin/bash ../libtool --tag=CXX --mode=compile g++ -DHAVE_CONFIG_H -I. -I.. -I../ -DPACKAGE_DATA_DIR=\""/usr/share"\" -DPACKAGE_LOCALE_DIR=\""/usr/share/locale"\" -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/libxml2 -Wdate-time -D_FORTIFY_SOURCE=2 -g -O2 -fdebug-prefix-map=/«PKGBUILDDIR»=. -fstack-protector-strong -Wformat -Werror=format-security -c -o MathStructure.lo MathStructure.cc
libtool: compile: g++ -DHAVE_CONFIG_H -I. -I.. -I../ -DPACKAGE_DATA_DIR=\"/usr/share\" -DPACKAGE_LOCALE_DIR=\"/usr/share/locale\" -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/libxml2 -Wdate-time -D_FORTIFY_SOURCE=2 -g -O2 -fdebug-prefix-map=/«PKGBUILDDIR»=. -fstack-protector-strong -Wformat -Werror=format-security -c MathStructure.cc -fPIC -DPIC -o .libs/MathStructure.o
In file included from /usr/include/c++/6/ext/hash_map:60:0,
                 from ../libqalculate/includes.h:40,
                 from MathStructure.h:15,
                 from MathStructure.cc:14:
/usr/include/c++/6/backward/backward_warning.h:32:2: warning: #warning This file includes at least one deprecated or antiquated header which may be removed without further notice at a future date. Please use a non-deprecated interface with equivalent functionality instead. For a listing of replacement headers and interfaces, consult the file backward_warning.h. To disable this warning use -Wno-deprecated. [-Wcpp]
 #warning \
  ^~~~~~~
MathStructure.cc: In function ‘bool sr_gcd(const MathStructure&, const MathStructure&, MathStructure&, std::vector<sym_desc>::const_iterator, const EvaluationOptions&)’:
MathStructure.cc:7166:53: error: no matching function for call to ‘MathStructure::gcd(MathStructure&, MathStructure&, MathStructure&, const EvaluationOptions&, bool)’
  MathStructure::gcd(cont_c, cont_d, gamma, eo, false);
                                                     ^
In file included from MathStructure.cc:14:0:
MathStructure.h:827:15: note: candidate: static bool MathStructure::gcd(const MathStructure&, const MathStructure&, MathStructure&, const EvaluationOptions&, MathStructure*, MathStructure*, bool)
   static bool gcd(const MathStructure &m1, const MathStructure &m2, MathStructure &mresult, const EvaluationOptions &eo, MathStructure *ca = NULL, MathStructure *cb = NULL, bool check_args = true);
               ^~~
MathStructure.h:827:15: note: no known conversion for argument 5 from ‘bool’ to ‘MathStructure*’
Makefile:531: recipe for target 'MathStructure.lo' failed