ProjectExplorer: Give Xcode clang higher priority than "bare" clang

If Xcode is present, we want its toolchain in the default kit, rather
than a generic compiler from /usr/bin.

Change-Id: If5d1dc02b6abcfff580162a19f07706d58681b7e
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/ios/iosconfigurations.cpp

@@ -587,6 +587,7 @@ Toolchains IosToolChainFactory::autoDetect(const ToolchainDetector &detector) co
             auto createOrAdd = [&](ClangToolChain *toolChain, Id l) {
                 if (!toolChain) {
                     toolChain = new ClangToolChain;
+                    toolChain->setPriority(ToolChain::PriorityHigh);
                     toolChain->setDetection(ToolChain::AutoDetection);
                     toolChain->setLanguage(l);
                     toolChain->setDisplayName(target.name);