package/gnutls: disable library search in /usr/lib

gnutls's configure script has a weird approach where it first searches
for dependent libraries in the path specified by --prefix, before
searching in the default search path. Since we set --prefix to /usr,
and it doesn't take into account DESTDIR (which is anyway not set at
configure time), that means it will first search /usr/lib before
searching $(STAGING_DIR)/usr/lib.

Ideally, this would be fixed in the configure script itself. However,
the m4 file that does this is pretty complex, it's not immediately clear
where to add $DESTDIR. In addition it comes from gnulib which is a
somewhat annoying upstream.

Therefore, instead, bypass the prefix lookup with
--without-libfoo-prefix. Note that we could set
--with-libfoo-prefix=$(STAGING_DIR)/usr (the latter is already done for
librt and libpthread), but that's pretty pointless -
--without-libfoo-prefix in fact reverts to what should have been done in
the first place, i.e. use the toolchain search path.

Add --without-libfoo-prefix for all options defined in configure (found
with ./configure --help | grep without-.*-prefix). Most of these are
only used in tests (e.g. libcrypto) or even not at all (e.g. libiconv),
but it's fairly hard to discover this and to be sure that they are
indeed not needed, so better pass all of them.

Remove the now-redundant arguments for librt and libpthread.

Add a comment to remind people to revisit these when bumping the
version.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Cc: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit b707a67daa31da6bd4bca19096c74febfd54375a)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/gnutls/gnutls.mk

@@ -4,6 +4,7 @@
 #
 ################################################################################
 
+# When bumping, make sure *all* --without-libfoo-prefix options are in GNUTLS_CONF_OPTS
 GNUTLS_VERSION_MAJOR = 3.7
 GNUTLS_VERSION = $(GNUTLS_VERSION_MAJOR).4
 GNUTLS_SOURCE = gnutls-$(GNUTLS_VERSION).tar.xz
@@ -26,7 +27,15 @@ GNUTLS_CONF_OPTS = \
 	--disable-tests \
 	--enable-local-libopts \
 	--enable-openssl-compatibility \
-	--with-librt-prefix=$(STAGING_DIR) \
+	--without-libcrypto-prefix \
+	--without-libdl-prefix \
+	--without-libev-prefix \
+	--without-libiconv-prefix \
+	--without-libintl-prefix \
+	--without-libpthread-prefix \
+	--without-libseccomp-prefix \
+	--without-librt-prefix \
+	--without-libz-prefix \
 	--without-tpm \
 	$(if $(BR2_PACKAGE_GNUTLS_OPENSSL),--enable,--disable)-openssl-compatibility \
 	$(if $(BR2_PACKAGE_GNUTLS_TOOLS),--enable-tools,--disable-tools) \
@@ -39,9 +48,6 @@ GNUTLS_CONF_ENV = gl_cv_socket_ipv6=yes \
 	gl_cv_func_gettimeofday_clobber=no
 GNUTLS_INSTALL_STAGING = YES
 
-# libpthread autodetection poison the linkpath
-GNUTLS_CONF_OPTS += $(if $(BR2_TOOLCHAIN_HAS_THREADS),--with-libpthread-prefix=$(STAGING_DIR)/usr)
-
 # gnutls needs libregex, but pcre can be used too
 # The check isn't cross-compile friendly
 GNUTLS_CONF_ENV += libopts_cv_with_libregex=yes
@@ -70,7 +76,6 @@ GNUTLS_CONF_OPTS += --without-p11-kit
 endif
 
 ifeq ($(BR2_PACKAGE_LIBUNISTRING),y)
-GNUTLS_CONF_OPTS += --with-libunistring-prefix=$(STAGING_DIR)/usr
 GNUTLS_DEPENDENCIES += libunistring
 else
 GNUTLS_CONF_OPTS += --with-included-unistring