re2: remove ARRAYSIZE macro

Change-Id: If39f8103bd88796bd91acfe74810f796f0e2332e
Reviewed-on: https://code-review.googlesource.com/1273
Reviewed-by: Russ Cox <rsc@swtch.com>
re2: more -Wno-sign-compare fixes

Change-Id: Ic0abc9ba4f3fd9767327b187e28d7624aaa20060
Reviewed-on: https://code-review.googlesource.com/1274
Reviewed-by: Russ Cox <rsc@swtch.com>
re2: more Gerrit+GitHub integration

Change-Id: I8c19cb4912d8e4bc8073b6f97279b2f57a59760c
Reviewed-on: https://code-review.googlesource.com/1275
Reviewed-by: Russ Cox <rsc@swtch.com>