Fix x86 slowpath getters and implement proxy.

The slowpath getters were using %eax to tell if an exception occurred,
instead of checking Thread->exception_. Also, proxy is implemented, and
run-test 004 works.

Change-Id: I0473635e093566a86d7deb54e715074373ff6d4b
diff --git a/src/asm_support.h b/src/asm_support.h
index 036e67c..e776e53 100644
--- a/src/asm_support.h
+++ b/src/asm_support.h
@@ -36,6 +36,8 @@
 #elif defined(__i386__)
 // Offset of field Thread::self_ verified in InitCpu
 #define THREAD_SELF_OFFSET 112
+// Offset of field Thread::exception_ verified in InitCpu
+#define THREAD_EXCEPTION_OFFSET 120
 #endif
 
 #endif  // ART_SRC_ASM_SUPPORT_H_