* Support 32-bit build.
Signatures/functions/imports/exports etc are defined as varuint32 in
the WebAssembly specification so use u32 rather than u64.
Decrease the static memory constants for 32-bit addressing mode so
that they fit within 32-bit memory constraints.
Conditionalize cmake compile of SignalHandlers.cpp so that -m32 is
passed when building 32-bit.
Add a no-op match for Reloc::X86CallPCRel4 during linking. This is
probably the wrong thing, but it allows the tests to pass. Using the
same logic from the Reloc::X86PCRel4 case did not work.
