It does feel a bit silly to have CONFIG_NR_CPUS at 64 and not have the other option needed to make this useful.
I've rebuilt the tinycore64 kernel with the following diff, and can confirm that it resolves the broken SMP,
there is however a slight size increase when enabling the option. In my personal opinion it makes sense to
enable this for the 64bit kernel configs.
--- ../config-4.2.9-tinycore64 2016-01-18 21:26:28.000000000 +0100
+++ .config 2016-05-27 11:26:33.097284521 +0200
@@ -355,7 +355,7 @@
-# CONFIG_X86_X2APIC is not set
# CONFIG_X86_EXTENDED_PLATFORM is not set
# CONFIG_X86_INTEL_LPSS is not set
-rw-r--r--. 1 root root 4024208 May 27 11:40 vmlinuz
-rw-r--r--. 1 root root 3807184 May 27 09:47 vmlinuz.orig