tell clang to not truncate macro backtraces
diff --git a/aos/build/aos.gypi b/aos/build/aos.gypi
index f6fefd5..dca03b3 100644
--- a/aos/build/aos.gypi
+++ b/aos/build/aos.gypi
@@ -308,6 +308,7 @@
                 'cflags': [
                   '-fcolor-diagnostics',
                   '-fmessage-length=80',
+                  '-fmacro-backtrace-limit=0',
                 ],
                 'defines': [
                   # This tells clang's optimizer the same thing.