yes that change TARGET_CPU="x86-64" to TARGET_CPU="silvermont" is correct but
then find line PROJECT_CFLAGS="-mmmx -msse -msse2 -mfpmath=sse" and change to PROJECT_CFLAGS=""
Why would you blank out $PROJECT_CFLAGS?
In my personal build, I replaced
TARGET_CPU="x86-64"
with
TARGET_CPU="silvermont"
and
PROJECT_CFLAGS="-mmmx -msse -msse2 -mfpmath=sse"
with
PROJECT_CFLAGS="-mmovbe -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -mpopcnt -maes -mpclmul -mrdrnd -mfpmath=sse"
So far all addons function. In fact I have noticed slightly lower memory usage, roughly 20-23% on average. However, I should state that I did not perform riguorus double-blind tests.
Oddly enough, before I implemented these changes Chromium produced choppy output from NetFlix videos. After the custom changes, Chromium produced better output. There is still a degree of dropped frames, but only during highly dynamic scenes (fast action on high quality videos). Which makes me wonder about recompiling Chromium with the same customizations...