Remove compiler warnings when building the emulator.

This forces -Wall during the build. Note that this patch doesn't
remove all warnings, but most of the remaining ones are from upstream anyway.

Change-Id: I8808d8495e99866e156ce5780d2e3c305eab491f
diff --git a/osdep.h b/osdep.h
index 1cdc7e2..b7e8d51 100644
--- a/osdep.h
+++ b/osdep.h
@@ -96,6 +96,8 @@
 int ffs(int i);
 
 int setenv(const char *name, const char *value, int overwrite);
+int asprintf(char **sptr, char *fmt, ...);
+int vasprintf(char **sptr, char *fmt, va_list args);
 
 typedef struct {
     long tv_sec;