s390: [wasm] Support 4GiB memories in Liftoff

Port 352e408b

Original Commit Message:

    Add codegen support for up to 4GiB memories in Liftoff code.

    This CL also adds three new mjsunit tests that stress large WASM
    memories (1, 2, and 4 GiB) and checks that accesses near these
    boundaries properly generate traps.

    Note there is still some trickiness around the setting of:
      1.) the flag --wasm-max-mem-pages
      2.) wasm-limits.h kSpecMaxWasmMemoryPages = 65536
      3.) wasm-limits.h kV8MaxWasmMemoryPages = 32767

    In particular, the allocation of memories is still limited to
    3.) and the runtime flag can only lower this limit.

    The above means that the tests for 2GiB and 4GiB memories will silently
    OOM by design until 3.) is changed (though they currently pass with
    manual testing). I argue it is better to include these tests up front,
    since they will immediately trigger if their memory allocation succeeds.

    Therefore the plan is to lift the restriction on 3.) after removing
    all other other internal V8 limitations including array buffers and views.

R=titzer@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=v8:7881
LOG=N

Change-Id: Ice70a9ac5a9a26b08cc77acb7deec98305574d01
Reviewed-on: https://chromium-review.googlesource.com/1167914
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55026}

src/wasm/baseline/s390/liftoff-assembler-s390.h

@@ -258,7 +258,11 @@ bool LiftoffAssembler::emit_i64_remu(LiftoffRegister dst, LiftoffRegister lhs,
 }
 
 void LiftoffAssembler::emit_i32_to_intptr(Register dst, Register src) {
-  UNREACHABLE();
+#ifdef V8_TARGET_ARCH_S390X
+  BAILOUT("emit_i32_to_intptr");
+#else
+// This is a nop on s390.
+#endif
 }
 
 bool LiftoffAssembler::emit_type_conversion(WasmOpcode opcode,