Make sure config.sub and config.guess are executable (#1024)

* Make sure config.sub and config.guess are executable

This fixes Spack build on ppc64 and aarch64, see https://github.com/spack/spack/pull/21256

* Move config files after setting their mode

Co-authored-by: Frank Denis <124872+jedisct1@users.noreply.github.com>

autogen.sh

@@ -106,10 +106,12 @@ fi
 
   curl -sSL --fail -o config.guess \
     'https://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.guess;hb=HEAD' &&
-    mv -f config.guess build-aux/config.guess
+    chmod +x config.guess &&
+    chmod +x build-aux/config.guess
 
   curl -sSL --fail -o config.sub \
     'https://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.sub;hb=HEAD' &&
+    chmod +x build-aux/config.sub &&
     mv -f config.sub build-aux/config.sub
 
   echo "Done."