./configure --help gives:
Code:
FONTCONFIG_CFLAGS
C compiler flags for FONTCONFIG, overriding pkg-config
FONTCONFIG_LIBS
linker flags for FONTCONFIG, overriding pkg-config
FREETYPE_CFLAGS
C compiler flags for FREETYPE, overriding pkg-config
FREETYPE_LIBS
linker flags for FREETYPE, overriding pkg-config
So it's to assume you have to work with FREETYPE_CFLAGS and FREETYPE_LIBS
PS: I've made a test compile and I believe it's FREETYPE_CFLAGS that you want.