Invoke generate_query_config.pl from the root

Otherwise it can't find headers to include.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/scripts/generate_query_config.pl b/scripts/generate_query_config.pl
index 61ea902..e99d633 100755
--- a/scripts/generate_query_config.pl
+++ b/scripts/generate_query_config.pl
@@ -49,6 +49,8 @@
           or die "No arguments supplied, must be run from project root or a first-level subdirectory\n";
     }
 }
+-f 'include/mbedtls/build_info.h'
+  or die "$0: must be run from project root, or from a first-level subdirectory with no arguments\n";
 
 # Excluded macros from the generated query_config.c. For example, macros that
 # have commas or function-like macros cannot be transformed into strings easily