pango_font_description_from_string not found

I'm building a program which uses GTK+3 and pango. Most of it compiles fine apart from the last bit which builds the executable. The final command is:

gcc -o z80sim main.c -Wall -Iz80 -Igui `pkg-config --cflags --libs gtk+-3.0`  obj/disas.o obj/iosim.o obj/sim0.o obj/sim1.o obj/sim2.o obj/sim3.o obj/sim4.o obj/sim5.o obj/sim6.o obj/sim7.o obj/simctl.o obj/simfun.o obj/simglb.o obj/simint.o obj/callbacks.o obj/code.o obj/guiglb.o obj/memory.o obj/flags.o obj/log.o obj/ports.o obj/registers.o

But I get this error message:

/usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/libgtk-3.so: undefined reference to symbol 'pango_font_description_from_string'
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/libpango-1.0.so: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status

I thought it was a matter of moving from GTK2 to 3, but when I checked libpango-1.0.a using nm I saw:

0000000000001670 T pango_font_description_from_string

So it is there. I wondered if the .so library is different from the .a, but I don't know how to check that.

Any suggestions?