cscppc: invoke cppcheck with -D__CPPCHECK__

... so that developers can conditionally provide simplified definitions
of their macros in cases where cppcheck would unnecessarily report false
positives on each use of the original macro definition.

Reported-by: Adrian Reber

cscppc.c

@@ -54,6 +54,7 @@ static const char *analyzer_def_arg_list[] = {
 #else
 #error "Unknown word size"
 #endif
+    "-D__CPPCHECK__",
     "--inline-suppr",
     "--quiet",
     "--template={file}:{line}: {severity}: {id}(CWE-{cwe}): {message}",