When checking target names, meson explictly forbids having multiple
targets with the same name. This is good, but it is strict and it is
impossible to have targets with the same basename and differing suffixes
(e.g. foo and foo.bin) in the same directory. Allow this for executables
by including the suffix (if it exists) in the interal target id. So foo
would be foo@exe and foo.bin would be foo.bin@exe.