Disable variables-big with debug binaries.

When compiled with SAFEMALLOC or with Windows
Debug CRT, it allocates and initializes 5GB of memory.
The effect is 20 minutes of paging and swapping on
a 4GB VM.

Still allow the test to run with optimized binaries.
Memory is not initialized in this case,  malloc() 
of 5GB  size will not bring the whole buffer into 
physical memory.

mysql-test/include/not_debug.inc

+let $is_debug = `select version() like '%debug%'`;
+if ($is_debug)
+{
+  skip Does not run in with debug binaries;
+}
+

mysql-test/t/variables-big.test

@@ -3,6 +3,10 @@
 #
 
 --source include/big_test.inc
+# The test would allocate and initialize 5GB of memory
+# if compiled with debug. It can take a lot of time
+# of for paging/swapping.
+--source include/not_debug.inc
 
 #
 # Bug#27322 failure to allocate transaction_prealloc_size causes crash