Add Libs.private and Requires.private to harfbuzz.pc

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=64501
diff --git a/src/Makefile.am b/src/Makefile.am
index 9d88c24..132683a 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -20,6 +20,8 @@
 
 HBCFLAGS =
 HBLIBS =
+HBNONPCLIBS =
+HBDEPS =
 HBSOURCES =  \
 	hb-atomic-private.hh \
 	hb-blob.cc \
@@ -133,12 +135,13 @@
 
 if HAVE_PTHREAD
 HBCFLAGS += $(PTHREAD_CFLAGS)
-HBLIBS   += $(PTHREAD_LIBS)
+HBNONPCLIBS += $(PTHREAD_LIBS)
 endif
 
 if HAVE_GLIB
 HBCFLAGS += $(GLIB_CFLAGS)
 HBLIBS   += $(GLIB_LIBS)
+HBDEPS   += $(GLIB_DEPS)
 HBSOURCES += hb-glib.cc
 HBHEADERS += hb-glib.h
 endif
@@ -146,6 +149,7 @@
 if HAVE_FREETYPE
 HBCFLAGS += $(FREETYPE_CFLAGS)
 HBLIBS   += $(FREETYPE_LIBS)
+HBDEPS   += $(FREETYPE_DEPS)
 HBSOURCES += hb-ft.cc
 HBHEADERS += hb-ft.h
 endif
@@ -153,20 +157,21 @@
 if HAVE_GRAPHITE2
 HBCFLAGS += $(GRAPHITE2_CFLAGS)
 HBLIBS   += $(GRAPHITE2_LIBS)
+HBDEPS   += $(GRAPHITE2_DEPS)
 HBSOURCES += hb-graphite2.cc
 HBHEADERS += hb-graphite2.h
 endif
 
 if HAVE_UNISCRIBE
 HBCFLAGS += $(UNISCRIBE_CFLAGS)
-HBLIBS   += $(UNISCRIBE_LIBS)
+HBNONPCLIBS += $(UNISCRIBE_LIBS)
 HBSOURCES += hb-uniscribe.cc
 HBHEADERS += hb-uniscribe.h
 endif
 
 if HAVE_CORETEXT
 HBCFLAGS += $(CORETEXT_CFLAGS)
-HBLIBS   += $(CORETEXT_LIBS)
+HBNONPCLIBS += $(CORETEXT_LIBS)
 HBSOURCES += hb-coretext.cc
 HBHEADERS += hb-coretext.h
 endif
@@ -182,6 +187,8 @@
 
 # Put the library together
 
+HBLIBS += $(HBNONPCLIBS)
+
 if OS_WIN32
 export_symbols = -export-symbols harfbuzz.def
 harfbuzz_def_dependency = harfbuzz.def
@@ -256,6 +263,8 @@
 		-e 's@%exec_prefix%@$(exec_prefix)@g' \
 		-e 's@%libdir%@$(libdir)@g' \
 		-e 's@%includedir%@$(includedir)@g' \
+		-e 's@%libs_private%@$(HBNONPCLIBS)@g' \
+		-e 's@%requires_private%@$(HBDEPS)@g' \
 		-e 's@%VERSION%@$(VERSION)@g' \
 	"$<" > "$@" \
 	|| ($(RM) "$@"; false)