autotools: Give in and force CONFIG_SHELL to bash

At present, CONFIG_SHELL becomes /bin/sh if its bash and /bin/bash if not. This
isn't deterministic and leads to changes in ptest packages which include Makefiles.

At first glance you'd think we'd hardcode to /bin/sh since most system shells are sane.

Sadly the dash vs. bash leads to quoting differences in configure.

The bash default is probably the safest option since configure tries to find bash
and this is what most systems would end up using.

The end result is a more consisent build environment.

[YOCTO #13752]

(From OE-Core rev: 33b1e27c29ed05da783f814cf9c3035675087ecc)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/autotools.bbclass

@@ -90,7 +90,7 @@ oe_runconf () {
 	cfgscript=`python3 -c "import os; print(os.path.relpath(os.path.dirname('${CONFIGURE_SCRIPT}'), '.'))"`/$cfgscript_name
 	if [ -x "$cfgscript" ] ; then
 		bbnote "Running $cfgscript ${CONFIGUREOPTS} ${EXTRA_OECONF} $@"
-		if ! ${CACHED_CONFIGUREVARS} $cfgscript ${CONFIGUREOPTS} ${EXTRA_OECONF} "$@"; then
+		if ! ${CACHED_CONFIGUREVARS} CONFIG_SHELL=/bin/bash $cfgscript ${CONFIGUREOPTS} ${EXTRA_OECONF} "$@"; then
 			bbnote "The following config.log files may provide further information."
 			bbnote `find ${B} -ignore_readdir_race -type f -name config.log`
 			bbfatal_log "configure failed"