ART: More warnings

Enable -Wno-conversion-null, -Wredundant-decls and -Wshadow in general,
and -Wunused-but-set-parameter for GCC builds.

Change-Id: I81bbdd762213444673c65d85edae594a523836e5
diff --git a/runtime/jdwp/jdwp_event.cc b/runtime/jdwp/jdwp_event.cc
index d1229b2..44f713c 100644
--- a/runtime/jdwp/jdwp_event.cc
+++ b/runtime/jdwp/jdwp_event.cc
@@ -138,7 +138,7 @@
     }
 }
 
-uint32_t GetInstrumentationEventFor(JdwpEventKind eventKind) {
+static uint32_t GetInstrumentationEventFor(JdwpEventKind eventKind) {
   switch (eventKind) {
     case EK_BREAKPOINT:
     case EK_SINGLE_STEP: