Fix building without system cairo, fontconfig, freetype, and harfbuzz

At least for me, this was needed when I added --without-system-cairo
--without-system-fontconfig --without-system-freetype
--without-system-harfbuzz to my otherwise fairly normal autogen.input
on Linux.

Change-Id: I149a57c24d6c11d710298125e53cb9524cb3dcaa
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/140001
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Reviewed-by: Tor Lillqvist <tml@collabora.com>

external/skia/Library_skia.mk

@@ -83,6 +83,7 @@ endif
 
 else
 $(eval $(call gb_Library_use_externals,skia,\
+    expat \
     freetype \
     fontconfig \
 ))

sdext/Executable_xpdfimport.mk

@@ -11,6 +11,8 @@ $(eval $(call gb_Executable_Executable,xpdfimport))
 
 $(eval $(call gb_Executable_use_externals,xpdfimport,\
     boost_headers \
+    expat \
+    freetype \
     poppler \
     $(if $(filter-out WNT MACOSX,$(OS)),fontconfig) \
     zlib \

vcl/Library_vcl.mk

@@ -81,6 +81,7 @@ $(eval $(call gb_Library_use_libraries,vcl,\
 
 $(eval $(call gb_Library_use_externals,vcl,\
     boost_headers \
+    expat \
     gio \
     glm_headers \
     graphite \

vcl/Library_vclplug_gen.mk

@@ -55,6 +55,7 @@ $(eval $(call gb_Library_use_externals,vclplug_gen,\
 	cairo \
 	graphite \
 	epoxy \
+	expat \
 	glm_headers \
 	harfbuzz \
 	icu_headers \