Use upstream utf8proc package, as suggested in
http://source.netsurf-browser.org/libutf8proc.git/commit/?id=770e329cceaf0620c7b482589a9b17ed1d19c16d

Work around upstream's lack of a pkg-config file and update API.

--- netsurf-3.6/Makefile
+++ netsurf-3.6/Makefile
@@ -527,10 +527,9 @@
 $(eval $(call pkg_config_find_and_add,libcss,CSS))
 $(eval $(call pkg_config_find_and_add,libdom,DOM))
 $(eval $(call pkg_config_find_and_add,libnsutils,nsutils))
-$(eval $(call pkg_config_find_and_add,libutf8proc,utf8proc))
 
 # Common libraries without pkg-config support
-LDFLAGS += -lz
+LDFLAGS += -lz -lutf8proc
 
 # Optional libraries with pkgconfig
 
--- netsurf-3.6/utils/idna.c
+++ netsurf-3.6/utils/idna.c
@@ -26,7 +26,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
-#include <libutf8proc/utf8proc.h>
+#include <utf8proc.h>
 
 #include "utils/errors.h"
 #include "utils/idna.h"
--- netsurf-3.7/test/Makefile	2017-10-15 08:39:24.000000000 -0500
+++ netsurf-3.7/test/Makefile	2017-11-05 11:14:46.219013218 -0600
@@ -139,14 +139,14 @@
 	-D_XOPEN_SOURCE=600 \
 	-Itest -Iinclude -Icontent/handlers -Ifrontends -I. -I.. \
 	-Dnsgtk \
-	$(shell pkg-config --cflags libcurl libparserutils libwapcaplet libdom libnsutils libutf8proc) \
+	$(shell pkg-config --cflags libcurl libparserutils libwapcaplet libdom libnsutils) \
 	$(LIB_CFLAGS)
 TESTCFLAGS := $(BASE_TESTCFLAGS) \
 	$(COV_CFLAGS) \
 	$(COV_CPPFLAGS)
 
 TESTLDFLAGS := -L$(TESTROOT) \
-	$(shell pkg-config --libs libcurl libparserutils libwapcaplet libdom libnsutils libutf8proc) -lz \
+	$(shell pkg-config --libs libcurl libparserutils libwapcaplet libdom libnsutils) -lz -lutf8proc \
 	$(LIB_LDFLAGS)\
 	$(COV_LDFLAGS)