S390: Fix incorrect V8_HOST_ARCH_S390X to V8_TARGET_ARCH_S390X

V8_HOST_ARCH_S390X doesn't exist but is incorrectly used. Therefore, preserved floating point registers are not being correctly saved/restored in JSEntryStub.

R=joransiu@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1865893002

Cr-Commit-Position: refs/heads/master@{#35311}

src/s390/code-stubs-s390.cc

@@ -1193,7 +1193,7 @@ void JSEntryStub::Generate(MacroAssembler* masm) {
   ProfileEntryHookStub::MaybeCallEntryHook(masm);
 
 // saving floating point registers
-#if V8_HOST_ARCH_S390X
+#if V8_TARGET_ARCH_S390X
   // 64bit ABI requires f8 to f15 be saved
   __ lay(sp, MemOperand(sp, -8 * kDoubleSize));
   __ std(d8, MemOperand(sp));
@@ -1355,7 +1355,7 @@ void JSEntryStub::Generate(MacroAssembler* masm) {
   __ la(sp, MemOperand(sp, 10 * kPointerSize));
 
 // saving floating point registers
-#if V8_HOST_ARCH_S390X
+#if V8_TARGET_ARCH_S390X
   // 64bit ABI requires f8 to f15 be saved
   __ ld(d8, MemOperand(sp));
   __ ld(d9, MemOperand(sp, 1 * kDoubleSize));