Move the declaration of query_config() to a dedicated header file

Declaring query_config() belongs with the query_config program, not in
ssl_test_lib.h, so move the declaration to a new header file
query_config.h.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

programs/test/query_compile_time_config.c

@@ -40,7 +40,7 @@
     "Mbed TLS build and the macro expansion of that configuration will be\n" \
     "printed (if any). Otherwise, 1 will be returned.\n"
 
-int query_config( const char *config );
+#include "query_config.h"
 
 int main( int argc, char *argv[] )
 {