Auto merge of #57953 - mati865:cc-fix, r=alexcrichton
Do not set CC, CFLAGS, CXX, CXXFLAGS, AR, RANLIB in bootstrap, it breaks cross compilation
Fixes https://github.com/rust-lang/rust/issues/57812
I tested it in AArch64 Ubuntu container with several days old tree to have all the tools buildable.
I did **not** test native builds (amd64 -> amd64), leaving it to CI.
r? @alexcrichton