Auto merge of #33651 - Nercury:update-i686-android-target-to-match-abi, r=alexcrichton

Update i686-linux-android features to match android x86 ABI.

Based on [android's official x86 ABI info](http://developer.android.com/ndk/guides/abis.html#x86), the x86 baseline CPU can be safely updated to `pentiumpro`, with the addition of `MMX`, `SSE`, `SSE2`, `SSE3`, `SSSE3` features.

r? @alexcrichton