Fix 'make test' detection when LANG is not in English

[adamjstewart]

Fixes #10487.

@weidendo can you test this?

We need to be careful here, as config.yaml provides a build_language setting that we don't want to overwrite.

[weidendo]

Thanks, works as expected here!
Excerpt with a Valgrind.spec which does trigger the default behaviour for a test with Autotools, ie. checking for target "test", then "check" (which does exist):

$ echo $LANG
de_DE.UTF-8
$ spack install -v --use-cache --test root valgrind~boost
...
==> RUN-TESTS: build-time tests [check]
==> 'make' '-j24' '-n' 'test'
==> Target 'test' not found in Makefile
==> 'make' '-j24' '-n' 'check'
==> 'make' '-j24' 'check'
...

[scheibelp]

Thanks!