[4.9] Switch gcc-4.9 to use google/gcc-4_9 branch.
This source drop uses svn version r212828 of google/gcc-4.9 branch.
We also cherry-picked r213062, r213063 and r213064 to fix windows
build issues.
All gcc-4.9 patches before July 3rd are ported to google/gcc-4.9.
The following prior commits has not been merged to google branch yet.
(They are included in this commit).
e7af147f979e657fe2df00808e5b4319b0e088c6,
baf87df3cb2683649ba7e9872362a7e721117c23, and
c231900e5dcc14d8296bd9f62b45997a49d4d5e7.

Change-Id: I4bea3ea470387ff751c2be4cb0d4a12059b9299b