SIMD.js Fix x87 build.

Rename method EmitIsSpecObject -> EmitIsSimdObject.

LOG=N
BUG=v8:4124

Review URL: https://codereview.chromium.org/1263473008

Cr-Commit-Position: refs/heads/master@{#29980}

src/full-codegen/x87/full-codegen-x87.cc

@@ -3313,7 +3313,7 @@ void FullCodeGenerator::EmitIsSpecObject(CallRuntime* expr) {
 }
 
 
-void FullCodeGenerator::EmitIsSpecObject(CallRuntime* expr) {
+void FullCodeGenerator::EmitIsSimdObject(CallRuntime* expr) {
   ZoneList<Expression*>* args = expr->arguments();
   DCHECK(args->length() == 1);