Don't build xserver with -I$(includedir) as it breaks cross-compiling

This is where to install headers to, not where to find headers to
build against. Toolchains should know where to locate their system
headers while non-system headers should be found using
pkg-config. Users with bizarre setups where the toolchain really
cannot find the system headers should set CPPFLAGS.

unix/xserver/hw/vnc/Makefile.am

 
 libvnccommon_la_CPPFLAGS = -DVENDOR_RELEASE="$(VENDOR_RELEASE)" -I$(TIGERVNC_SRCDIR)/unix/common \
 	-DVENDOR_STRING="\"$(VENDOR_STRING)\"" -I$(TIGERVNC_SRCDIR)/common -UHAVE_CONFIG_H \
-	-I$(TIGERVNC_SRCDIR)/unix/vncconfig $(XVNC_CPPFLAGS) ${XSERVERLIBS_CFLAGS} -I$(includedir) \
+	-I$(TIGERVNC_SRCDIR)/unix/vncconfig $(XVNC_CPPFLAGS) ${XSERVERLIBS_CFLAGS} \
 	-I$(top_srcdir)/include
 
 bin_PROGRAMS = Xvnc
 	-UHAVE_CONFIG_H \
 	-DXFree86Server -DVENDOR_RELEASE="$(VENDOR_RELEASE)" \
 	-DVENDOR_STRING="\"$(VENDOR_STRING)\"" -I$(TIGERVNC_SRCDIR)/common -I$(TIGERVNC_SRCDIR)/unix/common \
-	-I$(top_srcdir)/include ${XSERVERLIBS_CFLAGS} -I$(includedir)
+	-I$(top_srcdir)/include ${XSERVERLIBS_CFLAGS}
 
 Xvnc_LDADD = $(XVNC_LIBS) libvnccommon.la $(COMMON_LIBS) \
 	$(XSERVER_LIBS) $(XSERVER_SYS_LIBS) $(XVNC_SYS_LIBS) -lX11
 	-I$(top_srcdir)/hw/xfree86/os-support \
 	-I$(top_srcdir)/hw/xfree86/os-support/bus \
 	-I$(top_srcdir)/include \
-	${XSERVERLIBS_CFLAGS} -I$(includedir)
+	${XSERVERLIBS_CFLAGS}
 
 libvnc_la_LDFLAGS = -module -avoid-version -Wl,-z,now