avoid hardcoded pkg-config and includedir that doesn't pass a custom ROOT
--- a/gir/Makefile.am
+++ b/gir/Makefile.am
@@ -47,7 +47,7 @@ libanthygobject_1_0_la_LDFLAGS = \
 	-version-info @LT_VERSION_INFO@         \
 	$(NULL)
 
-ANTHY_INCLUDEDIR = $(shell pkg-config --variable=includedir $(ANTHY_PC))
+ANTHY_INCLUDEDIR = $(shell $(PKG_CONFIG) --cflags-only-I $(ANTHY_PC) | sed s/-I//)
 
 anthyincludedir = $(includedir)/ibus-anthy-1.0
 anthyinclude_HEADERS = \