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/Makefile.android b/Makefile.android
index 98968b9..70904f5 100644
--- a/Makefile.android
+++ b/Makefile.android
@@ -98,6 +98,11 @@
   endif
 endif
 
+# Enable warning, except those related to missing field initializers
+# (the QEMU coding style loves using these).
+#
+MY_CFLAGS += -Wall -Wno-missing-field-initializers
+
 include $(CLEAR_VARS)
 
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