configure: create the tests directory like the doc directory

This fixes an issue where the tests directory is not created for out of tree
builds before its needed
Tested-by: Dave Yeo <daveryeo@telus.net>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -5722,6 +5722,7 @@ enabled getenv || echo "#define getenv(x) NULL" >> $TMPH
 
 
 mkdir -p doc
+mkdir -p tests
 echo "@c auto-generated by configure" > doc/config.texi
 
 print_config ARCH_   "$config_files" $ARCH_LIST