Nim: Set targetAbi to Abi::hostAbi

Considering that you can link C libraries into the binary the
hostAbi is a better default than unknown-unknown-unknown-unknown.

Change-Id: I24ced24a2d04cdeb794d32c85a42bb848c7291ed
Reviewed-by: hjk <hjk@qt.io>

src/plugins/nim/project/nimtoolchain.cpp

@@ -66,7 +66,7 @@ QString NimToolChain::typeDisplayName() const
 
 Abi NimToolChain::targetAbi() const
 {
-    return Abi();
+    return Abi::hostAbi();
 }
 
 bool NimToolChain::isValid() const