The ebuild is calling tc-getPKGCONFIG instead of tc-getPKG_CONFIG. This is fixed in the masked ebuilds (3.6.x). This results in projects linking against armadillo to also have to explicitly link against blas and lapack (by default, armadillo wraps this for you), but since it cannot find those libraries due to this typo that is broken. I've attached a corrected version of the ebuild.
Created attachment 345010 [details] Corrected ebuild
Comment on attachment 345010 [details] Corrected ebuild --- armadillo-3.4.4.ebuild 2013-01-07 04:06:51.178921766 +0100 +++ - 2013-04-09 19:56:22.032022482 +0200 @@ -35,13 +35,13 @@ if use blas; then mycmakeargs+=( -DBLAS_FOUND=ON - -DBLAS_LIBRARIES="$($(tc-getPKGCONFIG) --libs blas)" + -DBLAS_LIBRARIES="$($(tc-getPKG_CONFIG) --libs blas)" ) fi if use lapack; then mycmakeargs+=( -DLAPACK_FOUND=ON - -DLAPACK_LIBRARIES="$($(tc-getPKGCONFIG) --libs lapack)" + -DLAPACK_LIBRARIES="$($(tc-getPKG_CONFIG) --libs lapack)" ) fi cmake-utils_src_configure
10 Apr 2013; Justin Lecher <jlec@gentoo.org> armadillo-3.4.4.ebuild, metadata.xml: Fix typo for pkg-config, #465292