Fix compilation with GCC 5.2

Fix compilation with GCC 5.2

Fixes:

../../test/cctest/compiler/test-js-typed-lowering.cc:224:14:
 error: ‘kJSTypes’ defined but not used [-Werror=unused-variable]
  static Type* kJSTypes[] = {Type::Undefined(), Type::Null(),   Type::Boolean(),

../../src/bignum.cc: In member function
 ‘void v8::internal::Bignum::AssignDecimalString(Vector<const char>)’:
  ../../src/bignum.cc:80:6: error: assuming signed overflow does not occur when
  assuming that (X + c) < X is always false [-Werror=strict-overflow]

../../src/compiler/ia32/code-generator-ia32.cc:1366:3:
  required from here ../../src/base/logging.h:123:26:
   error: comparison between signed and unsigned integer expressions
   [-Werror=sign-compare] DEFINE_CHECK_OP_IMPL(EQ, ==)

BUG=

Committed: https://crrev.com/e28183b5977a2d2732f7f8b9a2f26637c9566585
Cr-Commit-Position: refs/heads/master@{#31095}

[skomski, 2015-09-26 20:26:27]

The CQ bit was checked by karl@skomski.com to run a CQ dry run

[commit-bot: I haz the power, 2015-09-26 20:26:37]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1371823002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1371823002/1

[commit-bot: I haz the power, 2015-09-26 20:26:38]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-26 20:26:38]

Dry run: No L-G-T-M from a valid reviewer yet. Only full committers are
accepted.
Even if an L-G-T-M may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[skomski, 2015-10-05 08:59:07]

karl@skomski.com changed reviewers:
+ bmeurer@chromium.org

[Benedikt Meurer, 2015-10-05 10:18:58]

lgtm

[skomski, 2015-10-05 10:43:06]

The CQ bit was checked by karl@skomski.com

[commit-bot: I haz the power, 2015-10-05 10:43:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1371823002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1371823002/20001

[commit-bot: I haz the power, 2015-10-05 11:07:27]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-05 11:07:40]

Patchset 2 (id:??) landed as
https://crrev.com/e28183b5977a2d2732f7f8b9a2f26637c9566585
Cr-Commit-Position: refs/heads/master@{#31095}