enable -Werror=sign-compare in our Bazel build (pytorch#98671)

enable -Werror=sign-compare in our Bazel build

Summary:
This is already turned on for CMake, let's see what breaks.

Test Plan: Rely on CI.

Reviewers: sahanp

Subscribers:

Tasks:

Tags:

Pull Request resolved: pytorch#98671
Approved by: https://github.com/kit1980

.bazelrc

@@ -69,10 +69,6 @@ build --per_file_copt='^//.*\.(cpp|cc)$'@-Werror=all
 # The following warnings come from -Wall. We downgrade them from error
 # to warnings here.
 #
-# sign-compare has a tremendous amount of violations in the
-# codebase. It will be a lot of work to fix them, just disable it for
-# now.
-build --per_file_copt='^//.*\.(cpp|cc)$'@-Wno-sign-compare
 # We intentionally use #pragma unroll, which is compiler specific.
 build --per_file_copt='^//.*\.(cpp|cc)$'@-Wno-error=unknown-pragmas