clean-llvm needs a make target for x86_64-w64-mingw32

[thadguidry]

make[5]: Leaving directory /home/Thad/rust/llvm/i686-pc-mingw32/projects/sample /tools' make[4]: Leaving directory/home/Thad/rust/llvm/i686-pc-mingw32/projects/sample
'
make[3]: Leaving directory /home/Thad/rust/llvm/i686-pc-mingw32/projects' make[3]: Entering directory/home/Thad/rust/llvm/i686-pc-mingw32/bindings'
make[3]: Leaving directory /home/Thad/rust/llvm/i686-pc-mingw32/bindings' make[2]: Leaving directory/home/Thad/rust/llvm/i686-pc-mingw32'
make[1]: *** No rule to make target clean-llvmx86_64-w64-mingw32', needed byc
lean-llvm'. Stop.
make[1]: Leaving directory `/home/Thad/rust'
make: *** [rustllvm/llvm-auto-clean-stamp] Error 2

Thad@Thad-Windows ~/rust
$

[brson]

Looks like a bug in clean.mk.

We build compilers that run on 'host' triples, so for each host triple we must have an llvm - we don't need an llvm for 'target' triples, and in fact should not build one for targets that are not hosts - not all targets may be capable of running llvm.

The problem here is that clean.mk defines clean rules for all hosts, but then goes on to try to invoke them for all targets. The solution is probably to fix the latter to only invoke clean on host triples.

This is the same issue addressed by #7492

@thad for your purposes, since you are trying to create a compiler for x86_64 from an i686 host, you probably want to configure with --host-triples=i686-pc-mingw,x86_64-whatever, producing two complete compilers.