Use shared utf8proc library when USE_SYSTEM_UTF8PROC=1

Distribution policies strongly discourage statically linking
to libraries in packages. We thus need to allow using the
dynamic library when building packages.

Make.inc

@@ -354,7 +354,7 @@ endif
 endif
 
 ifeq ($(USE_SYSTEM_UTF8PROC), 1)
- LIBUTF8PROC = /usr/lib/libutf8proc.a
+ LIBUTF8PROC = -lutf8proc
 else
  LIBUTF8PROC = $(BUILD)/$(JL_LIBDIR)/libutf8proc.a
 endif