Generate harfbuzz-icu.pc

Currently it only works with ICU that has .pc files.  I'll
wait till someone complains before fixing it for icu-config
systems.
diff --git a/src/Makefile.am b/src/Makefile.am
index f7e7e9d..9334587 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -217,6 +217,8 @@
 EXTRA_libharfbuzz_la_DEPENDENCIES = $(harfbuzz_def_dependency)
 pkginclude_HEADERS = $(HBHEADERS)
 nodist_pkginclude_HEADERS = $(HBNODISTHEADERS)
+pkgconfigdir = $(libdir)/pkgconfig
+pkgconfig_DATA = harfbuzz.pc
 
 if HAVE_ICU
 lib_LTLIBRARIES += libharfbuzz-icu.la
@@ -225,8 +227,19 @@
 libharfbuzz_icu_la_LDFLAGS = $(AM_LDFLAGS) -version-info $(HB_LIBTOOL_VERSION_INFO) -no-undefined
 libharfbuzz_icu_la_LIBADD = $(ICU_LIBS) libharfbuzz.la
 pkginclude_HEADERS += hb-icu.h
+pkgconfig_DATA += harfbuzz-icu.pc
 endif
 
+%.pc: %.pc.in $(top_builddir)/config.status
+	$(AM_V_GEN) \
+	cat "$<" | \
+	$(SED) -e 's@%prefix%@$(prefix)@g;' | \
+	$(SED) -e 's@%exec_prefix%@$(exec_prefix)@g;' | \
+	$(SED) -e 's@%libdir%@$(libdir)@g;' | \
+	$(SED) -e 's@%includedir%@$(includedir)@g;' | \
+	$(SED) -e 's@%VERSION%@$(VERSION)@g;' | \
+	cat > "$@.tmp" && mv "$@.tmp" "$@" || ( $(RM) "$@.tmp"; false )
+
 
 CLEANFILES += harfbuzz.def
 harfbuzz.def: $(HBHEADERS) $(HBNODISTHEADERS)