Auto merge of #34083 - alexcrichton:dumb-hack, r=nrc
Auto merge of #34083 - alexcrichton:dumb-hack, r=nrc

rustc: Try to contain prepends to PATH

This commit attempts to bring our prepends to PATH on Windows when loading
plugins because we've been seeing quite a few issues with failing to spawn a
process on Windows, the leading theory of which is that PATH is too large as a
result of this. Currently this is mostly a stab in the dark as it's not
confirmed to actually fix the problem, but it's probably not a bad change to
have anyway!

cc #33844
Closes #17360

aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust