TESTNAME doesn't work with run-make tests

[huonw]

$ make check-stage2-rmake TESTNAME=smoke
maketest: bootstrap-from-c-with-green
maketest: bootstrap-from-c-with-native
maketest: c-dynamic-dylib
maketest: c-dynamic-rlib
maketest: c-link-to-rust-dylib
maketest: c-link-to-rust-staticlib
maketest: crate-data-smoke
maketest: c-static-dylib
maketest: c-static-rlib
maketest: dep-info
maketest: dep-info-custom
maketest: dylib-chain
maketest: lto-smoke
maketest: lto-smoke-c
maketest: mixing-deps
maketest: mixing-libs
maketest: no-intermediate-extras
maketest: prefer-dylib
maketest: prefer-rlib
maketest: prune-link-args
maketest: rlib-chain
maketest: rustdoc-hidden-line
maketest: rustdoc-smoke
maketest: simple-dylib
maketest: simple-rlib
maketest: static-unwinding

[alexcrichton]

This also doesn't work with doc tests (I've been sloppy lately, sadly)