gdbsupport: remove FUNCTION_NAME

__func__ is standard C++11:

    https://en.cppreference.com/w/cpp/language/function

Also, in C++11, __func__ expands to the demangled function name, so the
mention in the comment above FUNCTION_NAME doesn't apply anymore.
Finally, in places where FUNCTION_NAME is used, I think it's enough to
print the function name, no need to print the whole signature.
Therefore, I propose to just remove FUNCTION_NAME and update users to
use the standard __func__.

Change-Id: I778f28155422b044402442dc18d42d0cded1017d

gdbsupport/gdb_assert.h

@@ -33,29 +33,18 @@
 
 #define gdb_assert(expr)                                                      \
   ((void) ((expr) ? 0 :                                                       \
-	   (gdb_assert_fail (#expr, __FILE__, __LINE__, FUNCTION_NAME), 0)))
+	   (gdb_assert_fail (#expr, __FILE__, __LINE__, __func__), 0)))
 
 /* This prints an "Assertion failed" message, asking the user if they
    want to continue, dump core, or just exit.  */
-#if defined (FUNCTION_NAME)
 #define gdb_assert_fail(assertion, file, line, function)                      \
   internal_error (file, line, _("%s: Assertion `%s' failed."),                \
 		  function, assertion)
-#else
-#define gdb_assert_fail(assertion, file, line, function)                      \
-  internal_error (file, line, _("Assertion `%s' failed."),                    \
-		  assertion)
-#endif
 
 /* The canonical form of gdb_assert (0).
    MESSAGE is a string to include in the error message.  */
 
-#if defined (FUNCTION_NAME)
 #define gdb_assert_not_reached(message) \
-  internal_error (__FILE__, __LINE__, "%s: %s", FUNCTION_NAME, _(message))
-#else
-#define gdb_assert_not_reached(message) \
-  internal_error (__FILE__, __LINE__, _(message))
-#endif
+  internal_error (__FILE__, __LINE__, "%s: %s", __func__, _(message))
 
 #endif /* COMMON_GDB_ASSERT_H */