rustbuild: `test --stage 1 src/test/ui` builds "stage1 compiler artifacts"

[petrochenkov]

while other useful stage 1 tests like compile-fail or run-pass will happily run after building only "stage1 std artifacts".

compile-fail and ui are inseparable and need to be tested together and building "stage1 compiler artifacts" makes the edit-compile-test cycle ~twice longer.

[alexcrichton]

To do this we'd have to split the ui test suite between "requires only std" and "requires more than std". I believe there's one test which requires plugins, which needs to build the whole compiler

[petrochenkov]

Like compile-fail-fulldeps, but ui-fulldeps? (If understand the purpose of fulldeps tests correctly.)

[alexcrichton]

Indeed!