libidn2: Fix libunistring detection

libunistring is one such library which many autotooled packages
mistake to use from build system if its installed on it. This
is specifically toxic when build host arch is same as target arch
since we only see the problem during runtime but thankfully OE
has build time QA which warns about it.

QA Issue: libidn2: The compile log indicates that host include and/or library paths were used.

Using --with-libunistring-prefix nudges the autoconf system for the
component to first look into target sysroot before going on to search
on the build host

(From OE-Core rev: 9a4ea4ff856e2379888ea5cdcc0e761956e1f53b)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-extended/libidn/libidn2_2.0.5.bb

@@ -19,6 +19,10 @@ DEPENDS = "virtual/libiconv libunistring"
 
 inherit pkgconfig autotools gettext texinfo gtk-doc lib_package
 
+EXTRA_OECONF += "--disable-rpath \
+                 --with-libunistring-prefix=${STAGING_EXECPREFIXDIR} \
+                 "
+
 LICENSE_${PN} = "(GPLv2+ | LGPLv3)"
 LICENSE_${PN}-bin = "GPLv3+"