+ :COMPRESSION
+ This is only meaningful if the runtime was built with the :SB-CORE-COMPRESSION
+ feature enabled. If NIL (the default), saves to uncompressed core files. If
+ :SB-CORE-COMPRESSION was enabled at build-time, the argument may also be
+ an integer from -1 to 9, corresponding to zlib compression levels, or T
+ (which is equivalent to the default compression level, -1).
+