only define ARRAYSIZE_UNSAFE for NaCl builds

Now that C++11 is allowed, we can use arraysize instead of
ARRAYSIZE_UNSAFE, except in NaCl builds.  So let's move this
macro inside an NaCl ifdef.

BUG=chromium:405225
LOG=y
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/668303002

Patch from Mostyn Bramley-Moore <mostynb@opera.com>.

Cr-Commit-Position: refs/heads/master@{#24875}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24875 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/base/macros.h

@@ -25,6 +25,8 @@
   (reinterpret_cast<intptr_t>(&(reinterpret_cast<type*>(4)->field)) - 4)
 
 
+#if V8_OS_NACL
+
 // ARRAYSIZE_UNSAFE performs essentially the same calculation as arraysize,
 // but can be used on anonymous types or types defined inside
 // functions.  It's less safe than arraysize as it accepts some
@@ -65,9 +67,6 @@
   ((sizeof(a) / sizeof(*(a))) / \
    static_cast<size_t>(!(sizeof(a) % sizeof(*(a)))))  // NOLINT
 
-
-#if V8_OS_NACL
-
 // TODO(bmeurer): For some reason, the NaCl toolchain cannot handle the correct
 // definition of arraysize() below, so we have to use the unsafe version for
 // now.