internal/rosa: libffi artifact

Required by python during llvm test suite.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/llvm.go

@@ -125,6 +125,7 @@ func (t Toolchain) newLLVM(variant string, attr *llvmAttr) pkg.Artifact {
 	}
 
 	extra := []pkg.Artifact{
+		t.NewLibffi(),
 		t.NewPython(),
 		t.NewKernelHeaders(),
 	}