Currently on X87 platform we use only Double register (stack register) for Turbofan. So we directly

use 1 as allocatable Double register number when setting up the default register configuration..

It does not change the double register configuration of other platforms.

BUG=v8:4135
LOG=N

Review URL: https://codereview.chromium.org/1164813007

Cr-Commit-Position: refs/heads/master@{#29005}

src/compiler/register-configuration.cc

@@ -21,8 +21,13 @@ class ArchDefaultRegisterConfiguration : public RegisterConfiguration {
  public:
   ArchDefaultRegisterConfiguration()
       : RegisterConfiguration(Register::kMaxNumAllocatableRegisters,
+#if V8_TARGET_ARCH_X87
+                              1,
+                              1,
+#else
                               DoubleRegister::kMaxNumAllocatableRegisters,
                               DoubleRegister::NumAllocatableAliasedRegisters(),
+#endif
                               general_register_name_table_,
                               double_register_name_table_) {
     DCHECK_EQ(Register::kMaxNumAllocatableRegisters,