dev-php/PEAR-XML_ParserがEmergeできない

 *
 * Using dev-lang/php-5.2.6_rc1-r1
 *
 *
 * Using dev-lang/php-5.2.6_rc1-r1
 *
 * Checking for required PHP feature(s) ...
 *   Discovered missing USE flag: xml
 *
 * dev-lang/php-5.2.6_rc1-r1 needs to be re-installed with all of the following
 * USE flags enabled:
 *
 *   cli pcre xml zlib
 *
 *
 * ERROR: dev-php/PEAR-PEAR-1.6.2-r1 failed.
 * Call stack:
 *                   ebuild.sh, line   49:  Called pkg_setup
 *   PEAR-PEAR-1.6.2-r1.ebuild, line   43:  Called require_php_with_use 'pkg_setup' 'pkg_setup' 'pkg_setup' 'cli'
 *           depend.php.eclass, line  285:  Called die
 * The specific snippet of code:
 *              die "Missing PHP USE flags found"
 *  The die message:
 *   Missing PHP USE flags found
 *
 * 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/dev-php/PEAR-PEAR-1.6.2-r1/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/dev-php/PEAR-PEAR-1.6.2-r1/temp/die.env'.
 *

こんなエラーメッセージが出てきたときは

/etc/make.conf
USE="cli pcre xml zlib"

を追加しておいて（もしくはUSE="cli pcre xml zlib" emerge）
phpをnewuseしてemergeでその後XML_ParserをEmergeすればOK!