To resolve:

/bin/grep: /usr/lib/libcairo.la: No such file or directory
/usr/bin/sed: can't read /usr/lib/libcairo.la: No such file or directory
libtool: link: `/usr/lib/libcairo.la' is not a valid libtool archive
make[2]: *** [librsvg-2.la] Error 1
make[2]: Leaving directory `/var/tmp/portage/gnome-base/librsvg-2.34.1-r1/work/librsvg-2.34.1'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/var/tmp/portage/gnome-base/librsvg-2.34.1-r1/work/librsvg-2.34.1'
make: *** [all] Error 2
 * ERROR: gnome-base/librsvg-2.34.1-r1 failed (compile phase):
 *   emake failed
 * 
 * If you need support, post the output of 'emerge --info =gnome-base/librsvg-2.34.1-r1',
 * the complete build log and the output of 'emerge -pqv =gnome-base/librsvg-2.34.1-r1'.
 * The complete build log is located at '/var/tmp/portage/gnome-base/librsvg-2.34.1-r1/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/gnome-base/librsvg-2.34.1-r1/temp/environment'.
 * S: '/var/tmp/portage/gnome-base/librsvg-2.34.1-r1/work/librsvg-2.34.1'

Emerge lafilefixer if you do not already have it installed:

# emerge lafilefixer

Now run:

# lafilefixer --justfixit