i dont know if this is an actual bug since i cant find any documentation on ALLOWED_FLAGS but it looks like the line below is filtering -Os and judging by the flags that are listed it seems like -Os should not be filtered. the following line is from the xfree-4.3.0-r4 ebuild and is also in the 4.3.99.902-r1. ALLOWED_FLAGS="-fstack-protector -march -mcpu -O -O1 -O2 -O3 -pipe"
*** This bug has been marked as a duplicate of 12775 ***