CPP: Modify similar query as well.

Author: geoffw0

cpp/ql/src/Power of 10/Rule 6/GlobalCouldBeStatic.ql

@@ -12,5 +12,6 @@ from GlobalVariable v
 where forex(VariableAccess va | va.getTarget() = v | va.getFile() = v.getDefinitionLocation().getFile())
       and not v.hasSpecifier("static")
       and strictcount(v.getAnAccess().getEnclosingFunction()) > 1 // If = 1, variable should be function-scope.
+      and not v.getADeclarationEntry().getFile() instanceof HeaderFile // intended to be accessed elsewhere
 select v, "The global variable " + v.getName() + " is not accessed outside of " + v.getFile().getBaseName() +
       " and could be made static."