pkg-autotools: add support for <pkg>_AUTORECONF_ENV

This commit improves the autotools-package infrastructure to support a
<pkg>_AUTORECONF_ENV variable, which allows a package maintainer to
pass additional variables in the environment of the autoreconf
execution. This is useful in the situation where configure.ac contains
shell commands using environment variables that are only executed when
autoreconf is run.

Signed-off-by: Rick Taylor <rick.taylor@cassidian.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

docs/manual/adding-packages-autotools.txt

@@ -121,6 +121,11 @@ cases, typical packages will therefore only use a few of them.
   automake, libtool, etc.). Valid values are +YES+ and
   +NO+. By default, the value is +NO+
 
+* +LIBFOO_AUTORECONF_ENV+, to specify additional environment
+  variables to pass to the 'autoreconf' program if
+  +LIBFOO_AUTORECONF=YES+. These are passed in the environment of
+  the 'autoreconf' command. By default, empty.
+  
 * +LIBFOO_AUTORECONF_OPT+ to specify additional options
   passed to the 'autoreconf' program if
   +LIBFOO_AUTORECONF=YES+. By default, empty.

package/pkg-autotools.mk

@@ -224,7 +224,7 @@ endef
 #
 define AUTORECONF_HOOK
 	@$$(call MESSAGE,"Autoreconfiguring")
-	$$(Q)cd $$($$(PKG)_SRCDIR) && $$(AUTORECONF) $$($$(PKG)_AUTORECONF_OPT)
+	$$(Q)cd $$($$(PKG)_SRCDIR) && $$($$(PKG)_AUTORECONF_ENV) $$(AUTORECONF) $$($$(PKG)_AUTORECONF_OPT)
 	$$(Q)if test "$$($$(PKG)_LIBTOOL_PATCH)" = "YES"; then \
 		for i in `find $$($$(PKG)_SRCDIR) -name ltmain.sh`; do \
 			ltmain_version=`sed -n '/^[ 	]*VERSION=/{s/^[ 	]*VERSION=//;p;q;}' $$$$i | \