tools: Provide a definition of WARN_ON

The definition of WARN_ON being used by the radix tree test suite was
deficient in two ways: it did not provide a return value, and it stopped
execution instead of continuing.  This version of WARN_ON tells you
which file & line the assertion was triggered in.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>

tools/testing/radix-tree/linux/kernel.h

@@ -24,7 +24,6 @@
 #endif
 
 #define BUG_ON(expr)	assert(!(expr))
-#define WARN_ON(expr)	assert(!(expr))
 #define __init
 #define __must_check
 #define panic(expr)