Auto merge of #38394 - alexcrichton:fix-nightlies, r=brson
Auto merge of #38394 - alexcrichton:fix-nightlies, r=brson

rustbuild: Package rust-mingw by default

This fixes the `make dist` step on MinGW to package the `rust-mingw` component
by default. This should hopefully be the last step in fixing nightlies.

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