Disable confcache in /etc/make.conf if you are getting this when trying to emerge device-mapper.1.02.19 on Gentoo:
checking target system type… config.sub: missing argument
Try `config.sub –help’ for more information.
configure: error: /bin/sh autoconf/config.sub  failed
!!! Please attach the following file when filing a report to bugs.gentoo.org:
!!! /var/tmp/portage/sys-fs/device-mapper-1.02.19/work/device-mapper.1.02.19/config.log
!!! ERROR: sys-fs/device-mapper-1.02.19 failed.
Call stack:
  ebuild.sh, line 1621:   Called dyn_compile
  ebuild.sh, line 973:   Called qa_call ‘src_compile’
  ebuild.sh, line 44:   Called src_compile
  device-mapper-1.02.19.ebuild, line 22:   Called econf ‘–sbindir=/sbin’ ‘–disable-selinux’
  ebuild.sh, line 578:   Called die
!!! econf failed
!!! If you need support, post the topmost build error, and the call stack if relevant.
!!! A complete build log is located at ‘/var/tmp/portage/sys-fs/device-mapper-1.02.19/temp/build.log’.