[libsampler] Remove support for old OS X versions

OS X has been a UNIX 03 registered product since version 10.5,
released in October 2007.

Bug: v8:8834
Change-Id: I64ca5512a9999b6eb7b4003a6758081a06eb6529
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1569437
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60891}

src/libsampler/sampler.cc

@@ -436,25 +436,13 @@ void SignalHandler::FillRegisterState(void* context, RegisterState* state) {
 #endif  // V8_HOST_ARCH_*
 #elif V8_OS_MACOSX
 #if V8_HOST_ARCH_X64
-#if __DARWIN_UNIX03
   state->pc = reinterpret_cast<void*>(mcontext->__ss.__rip);
   state->sp = reinterpret_cast<void*>(mcontext->__ss.__rsp);
   state->fp = reinterpret_cast<void*>(mcontext->__ss.__rbp);
-#else  // !__DARWIN_UNIX03
-  state->pc = reinterpret_cast<void*>(mcontext->ss.rip);
-  state->sp = reinterpret_cast<void*>(mcontext->ss.rsp);
-  state->fp = reinterpret_cast<void*>(mcontext->ss.rbp);
-#endif  // __DARWIN_UNIX03
 #elif V8_HOST_ARCH_IA32
-#if __DARWIN_UNIX03
   state->pc = reinterpret_cast<void*>(mcontext->__ss.__eip);
   state->sp = reinterpret_cast<void*>(mcontext->__ss.__esp);
   state->fp = reinterpret_cast<void*>(mcontext->__ss.__ebp);
-#else  // !__DARWIN_UNIX03
-  state->pc = reinterpret_cast<void*>(mcontext->ss.eip);
-  state->sp = reinterpret_cast<void*>(mcontext->ss.esp);
-  state->fp = reinterpret_cast<void*>(mcontext->ss.ebp);
-#endif  // __DARWIN_UNIX03
 #endif  // V8_HOST_ARCH_IA32
 #elif V8_OS_FREEBSD
 #if V8_HOST_ARCH_IA32