Set aside fixnums in GCL
(Allocate-fixnum-range fixnum-lo fixnum-hi) causes Gnu Common
(GCL) to create a persistent table for the integers between fixnum-lo and
fixnum-hi (both bounds inclusive). This table is referenced first when
any integer is boxed and the existing box in the table is used if the integer
is in bounds. This can speed up GCL considerably by avoiding wasteful fixnum
boxing. Here, fixnum-lo and fixnum-hi should be fixnums. On 32-bit
machines it would be good for them to be of type (signed-byte 30), with
fixnum-lo <= fixnum-hi.
When this function is executed in a Lisp implementation other than GCL, it
has no side effect. This function always returns nil.