fate: add support for specifying the shell used to run configure

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

tests/fate.sh

@@ -41,7 +41,7 @@ update()(
 
 configure()(
     cd ${build} || return
-    ${src}/configure                                                    \
+    ${shell} ${src}/configure                                           \
         --prefix="${inst}"                                              \
         --samples="${samples}"                                          \
         --enable-gpl                                                    \