When checking for libEMF, configure.in (dia-0.97.2, and similar in git master) has line 224:

	CPPFLAGS="${CPPFLAGS} -I /usr/include/libEMF"

And then a few lines later:

		LIBEMF_CFLAGS='-I /usr/include/libEMF'

First, it's not correct to have whitespace between the -I flag and the pathname (syntax mistake that "some" compilers tolerate).

But it's also logically flawed because it assumes my libEMF is part of my vendor base system (rather than in /usr/local or some other location). That library appears to keep all its headers in the libEMF subdir. But also it appears to know that, and emf.h loads its other .h with that subdir (for example #include <libEMF/wine/windef.h>), so that extra -I shouldn't be needed if dia accesses emf.h as libEMF/emf.h directly.