module_param: add __same_type convenience wrapper for __builtin_types_compatible_p

Impact: new API

__builtin_types_compatible_p() is a little awkward to use: it takes two
types rather than types or variables, and it's just damn long.

(typeof(type) == type, so this works on types as well as vars).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

include/linux/compiler.h

@@ -261,6 +261,11 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
 # define __section(S) __attribute__ ((__section__(#S)))
 #endif
 
+/* Are two types/vars the same type (ignoring qualifiers)? */
+#ifndef __same_type
+# define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
+#endif
+
 /*
  * Prevent the compiler from merging or refetching accesses.  The compiler
  * is also forbidden from reordering successive instances of ACCESS_ONCE(),