Problems compiling

I’m trying to compile code from https://github.com/mtorromeo/gmenu2x using a
cross-compiler, and am getting fatal errors compiling src/fonthelper.cpp:

src/fonthelper.cpp: In constructor ‘FontHelper::FontHelper(const
std::string&, int, RGBAColor, RGBAColor)’:
src/fonthelper.cpp:26: error: ‘TTF_HINTING_NORMAL’ was not declared in this
scope
src/fonthelper.cpp:26: error: ‘TTF_SetFontHinting’ was not declared in this
scope
src/fonthelper.cpp:28: error: ‘TTF_SetFontOutline’ was not declared in this
scope
make: *** [objs/wiz/src/fonthelper.o] Error 1

I also tried compiling natively in Ubuntu to see if it was a toolchain
problem, and I get a similar error:

src/fonthelper.cpp: In constructor ?FontHelper::FontHelper(const
std::string&, int, RGBAColor, RGBAColor)?:
src/fonthelper.cpp:26: error: ?TTF_HINTING_NORMAL? was not declared in this
scope
src/fonthelper.cpp:26: error: ?TTF_SetFontHinting? was not declared in this
scope
src/fonthelper.cpp:28: error: ?TTF_SetFontOutline? was not declared in this
scope
make: *** [objs/pc/src/fonthelper.o] Error 1

The SDL-ttf docs mention that those constants are supposed to be defined, so
I’m confused as to why they are not defined in, nor defined indirectly by
SDL_ttf.h. Anyone know what the problem could be?

Thanks.