Make the arm port build cleanly with Clang.

Make the arm port build cleanly with Clang.

This fixes the following two warnings, so that "make all" builds cleanly
with Clang:

  src/arm/macro-assembler-arm.h:1410:7: error: private field
  'instructions_' is not used
        [-Werror,-Wunused-private-field]
          int instructions_;  // Number of instructions of the expected patch size.
              ^

  src/arm/simulator-arm.cc:402:20: error: variable 'words' is used uninitialized whenever 'if'
        condition is false [-Werror,-Wsometimes-uninitialized]
          } else if (argc == next_arg + 1) {
                     ^~~~~~~~~~~~~~~~~~~~
  ../src/arm/simulator-arm.cc:407:21: note: uninitialized use occurs here
          end = cur + words;
                      ^~~~~
  ../src/arm/simulator-arm.cc:402:16: note: remove the 'if' if its condition is always true
          } else if (argc == next_arg + 1) {
                 ^~~~~~~~~~~~~~~~~~~~~~~~~~

Committed: https://code.google.com/p/v8/source/detail?r=13583

[ulan, 2013-02-04 10:01:36]

LGTM, I will land it for you.

[ulan, 2013-02-04 10:31:02]

Committed manually as r13583 (presubmit successful).