When installing a number of packages - such as wireshark - that require but do not include libgcrypt as a dependency:

packet-ssl-utils.h:37:20: fatal error: gcrypt.h: No such file or directory
compilation terminated.
make[5]: *** [libdissectors_la-packet-dtls.lo] Error 1
make[5]: Leaving directory `/var/tmp/portage/net-analyzer/wireshark-1.6.6/work/wireshark-1.6.6/epan/dissectors'
make[4]: *** [all-recursive] Error 1
make[4]: Leaving directory `/var/tmp/portage/net-analyzer/wireshark-1.6.6/work/wireshark-1.6.6/epan/dissectors'
make[3]: *** [all] Error 2
make[3]: Leaving directory `/var/tmp/portage/net-analyzer/wireshark-1.6.6/work/wireshark-1.6.6/epan/dissectors'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/var/tmp/portage/net-analyzer/wireshark-1.6.6/work/wireshark-1.6.6/epan'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/var/tmp/portage/net-analyzer/wireshark-1.6.6/work/wireshark-1.6.6'
make: *** [all] Error 2
emake failed
 * ERROR: net-analyzer/wireshark-1.6.6 failed (compile phase):
 *   (no error message)
 * 
 * Call stack:
 *     ebuild.sh, line  85:  Called src_compile
 *   environment, line 5192:  Called die
 * The specific snippet of code:
 *       emake || die;
 * 
 * If you need support, post the output of 'emerge --info =net-analyzer/wireshark-1.6.6',
 * the complete build log and the output of 'emerge -pqv =net-analyzer/wireshark-1.6.6'.
 * The complete build log is located at '/var/tmp/portage/net-analyzer/wireshark-1.6.6/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/net-analyzer/wireshark-1.6.6/temp/environment'.
 * S: '/var/tmp/portage/net-analyzer/wireshark-1.6.6/work/wireshark-1.6.6'

Emerge it independently and be sure to keep it in your /var/lib/portage/world list if you ever do cleanup:

# emerge libgcrypt --ask

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

Calculating dependencies... done!
[ebuild  N     ] dev-libs/libgpg-error-1.10  USE="nls -common-lisp -static-libs" 
[ebuild  N     ] dev-libs/libgcrypt-1.4.6  USE="-static-libs" 

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