Fix CPU(32BIT) definition

Previously WTF_CPU_32BIT definition is inside #if of ARM.
This CL make CPU(32BIT) true on all architectures if and only if not CPU(64BIT).

BUG=432033

Review URL: https://codereview.chromium.org/712303003

git-svn-id: svn://svn.chromium.org/blink/trunk@185196 bbb929c8-8fbe-4397-9dbb-9b2b20218538