Clang buildfixes

Building with clang took a few very small changes. The change to
helper/log.h is because clang doesn't like an expression where the
result is unused. In helper/system.h, I just defined true and false
since clang doesn't have them builtin.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

src/helper/system.h

@@ -85,4 +85,9 @@
 #include <fcntl.h>
 #endif
 
+#ifndef true
+#define true	1
+#define false	0
+#endif
+
 #endif // SYSTEM_H