root@localhost test # emerge pecl-pdo-mysql
Calculating dependencies... done!
>>> Emerging (1 of 2) dev-php5/pecl-pdo-1.0.2 to /
>>> Downloading http://ftp.belnet.be/packages/gentoo/distfiles/PDO-1.0.2.tgz
--13:45:48--  http://ftp.belnet.be/packages/gentoo/distfiles/PDO-1.0.2.tgz
           => `/usr/portage/distfiles/PDO-1.0.2.tgz'
Resolving ftp.belnet.be... 193.190.198.20, 2001:6a8:3c80:0:203:baff:fe39:f931
Connecting to ftp.belnet.be|193.190.198.20|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 49,810 (49K) [application/x-gzip]

100%[===================================================================================>] 49,810        --.--K/s             

13:45:48 (397.89 KB/s) - `/usr/portage/distfiles/PDO-1.0.2.tgz' saved [49810/49810]

>>> checking ebuild checksums ;-)
>>> checking auxfile checksums ;-)
>>> checking miscfile checksums ;-)
>>> checking PDO-1.0.2.tgz ;-)
 * 
 * Using dev-lang/php-5.1.4-r4
 * 
 * 
 * You have built dev-lang/php-5.1.4-r4 to use the bundled PDO support.
 * If you want to use the PECL PDO packages, you must rebuild
 * your PHP with the 'pdo-external' USE flag instead.
 * 

!!! ERROR: dev-php5/pecl-pdo-1.0.2 failed.
Call stack:
  ebuild.sh, line 1555:   Called dyn_setup
  ebuild.sh, line 668:   Called pkg_setup
  pecl-pdo-1.0.2.ebuild, line 39:   Called die

!!! PHP built to use bundled PDO support
!!! If you need support, post the topmost build error, and the call stack if relevant.