Update the disallowed copy/assign in the mutex code.
Update the disallowed copy/assign in the mutex code.

Change-Id: I1fcc6af6b69f537f6528396e27f4d809fa432ee5
Reviewed-on: https://code-review.googlesource.com/6834
Reviewed-by: Paul Wankadia <62d4e38bb1380f055ec4b899baa75e52af09c5f7@google.com>

google/re2,google/re2,google/re2,google/re2,google/re2