These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild  N    *] sys-kernel/spl-9999  USE="-custom-cflags -debug" 0 kB
[ebuild  N    *] sys-fs/zfs-9999  USE="-custom-cflags -debug -dracut -static-libs -test -test-suite" 0 kB

Total: 2 packages (2 new), Size of downloads: 0 kB

Would you like to merge these packages? [Yes/No] y

>>> Verifying ebuild manifests

>>> Starting parallel fetch

>>> Emerging (1 of 2) sys-kernel/spl-9999
openpty failed: 'out of pty devices'
 * Determining the location of the kernel source code
 * Found kernel source directory:
 *     /usr/src/linux
 * Found sources for kernel version:
 *     3.2.12-gentoo-LAPTOPGEN
 * Checking for suitable kernel configuration options...
 *   CONFIG_ZLIB_DEFLATE:        is not set when it should be.
 * Please check to make sure these options are set correctly.
 * Failure to do so may cause unexpected problems.
 * Once you have satisfied these options, please try merging
 * this package again.
 * ERROR: sys-kernel/spl-9999 failed (setup phase):
 *   Incorrect kernel configuration options
 *
 * Call stack:
 *           ebuild.sh, line  85:  Called pkg_setup
 *     spl-9999.ebuild, line  35:  Called check_extra_config
 *   linux-info.eclass, line 783:  Called die
 * The specific snippet of code:
 *              die "Incorrect kernel configuration options"
 *
 * If you need support, post the output of 'emerge --info =sys-kernel/spl-9999',
 * the complete build log and the output of 'emerge -pqv =sys-kernel/spl-9999'.
 * The complete build log is located at '/var/tmp/portage/sys-kernel/spl-9999/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/sys-kernel/spl-9999/temp/die.env'.
 * S: '/var/tmp/portage/sys-kernel/spl-9999/work/spl-9999'

>>> Failed to emerge sys-kernel/spl-9999, Log file:

>>>  '/var/tmp/portage/sys-kernel/spl-9999/temp/build.log'

 * Messages for package sys-kernel/spl-9999:

 *   CONFIG_ZLIB_DEFLATE:        is not set when it should be.
 * Please check to make sure these options are set correctly.
 * Failure to do so may cause unexpected problems.
 * Once you have satisfied these options, please try merging
 * this package again.
 * ERROR: sys-kernel/spl-9999 failed (setup phase):
 *   Incorrect kernel configuration options
 *
 * Call stack:
 *           ebuild.sh, line  85:  Called pkg_setup
 *     spl-9999.ebuild, line  35:  Called check_extra_config
 *   linux-info.eclass, line 783:  Called die
 * The specific snippet of code:
 *              die "Incorrect kernel configuration options"
 *
 * If you need support, post the output of 'emerge --info =sys-kernel/spl-9999',
 * the complete build log and the output of 'emerge -pqv =sys-kernel/spl-9999'.
 * The complete build log is located at '/var/tmp/portage/sys-kernel/spl-9999/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/sys-kernel/spl-9999/temp/die.env'.
 * S: '/var/tmp/portage/sys-kernel/spl-9999/work/spl-9999'