OS-4368 lxbrand glibc abhors CPUID limits

@@ -39,10 +39,15 @@
 
        See the processor manufacturers documentation for further information
        about the syntax and semantics of the wide variety of information
        available from this instruction.
 
+       Some systems can be configured to limit the cpuid opcodes which are
+       accessible.  While illumos handles this condition, other software may
+       malfunction when such limits are enabled.  Those settings are typically
+       manipulated in the BIOS.
+
 EXAMPLE
        This example allows you to determine if the current x86 processor
        supports "long mode," which is a necessary (but not sufficient)
        condition for running the 64-bit Solaris kernel on the processor.