X87: Make --always-opt also optimize top-level code

port 2d281e71 (r27633)

original commit message:

    Make --always-opt also optimize top-level code.

    This enables eager optimization of top-level code with TurboFan and
    extends test coverage by triggering it with the --always-opt flag.
    Script contexts are now also properly allocated in TurboFan.

BUG=

Review URL: https://codereview.chromium.org/1077523002

Cr-Commit-Position: refs/heads/master@{#27693}

src/x87/lithium-codegen-x87.cc

@@ -224,6 +224,7 @@ bool LCodeGen::GeneratePrologue() {
     Comment(";;; Allocate local context");
     bool need_write_barrier = true;
     // Argument to NewContext is the function, which is still in edi.
+    DCHECK(!info()->scope()->is_script_scope());
     if (heap_slots <= FastNewContextStub::kMaximumSlots) {
       FastNewContextStub stub(isolate(), heap_slots);
       __ CallStub(&stub);