apr-native: Set CONFIG_SHELL to /bin/bash

The apr-native provides usr/share/build-1/libtool which is required by
the recipe such as apache2-native. If we don't set the CONFIG_SHELL to
/bin/bash, then:

1) If we build apr-native on a host which is "/bin/sh -> bash", the
   interpreter in usr/share/build-1/libtool would be "#!/bin/sh".
2) When we re-use apr-native's sstate on a host which is
   "/bin/sh -> dash", there would be errors.

(From OE-Core rev: 38d83009dfe77437533969ce681605a9ab9534ac)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-support/apr/apr_1.5.1.bb

@@ -86,3 +86,5 @@ do_install_ptest() {
 	cp ${S}/test/testall $t/
 	cp ${S}/test/tryread $t/
 }
+
+export CONFIG_SHELL="/bin/bash"