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Fix Solaris compilation (#1499) (#1500)

This patch fixes compilation on Solaris, addressing the problems reported
in Issue #1499:

* Provide `HOST_NAME_MAX` definition.
* Match `sysconf(3C)` return type.
* Avoid `-Wcast-qual` warnings with `libkstat(3KSTAT)` functions.
* Avoid clash with `<floatingpoint.h>` `single` typedef.