Rollup merge of #137882 - onur-ozkan:remove-extra-compiler-stage, r=Kobzol

do not build additional stage on compiler paths

When calling `x build compiler (or rustc) --stage N` bootstrap builds stage N+1 compiler, which is clearly not what we requested. This doesn't happen when running `x build --stage N` without explicitly targeting the compiler.

The changes applied fix this issue.

r? ghost

Author: matthiaskrgr