Clang: Add CLANG-UPGRADE-CHECK marker

...for things to watch out on an upgrade.

Change-Id: I75b77a3c8fa238939b625d084c7db220ab429319
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangstaticanalyzer/clangstaticanalyzerutils.h

@@ -45,6 +45,7 @@ QString clangExecutableFromSettings(Core::Id toolchainType, bool *isValid);
 
 QString createFullLocationString(const Debugger::DiagnosticLocation &location);
 
+// CLANG-UPGRADE-CHECK: Adapt minimum version numbers.
 class ClangExecutableVersion : public QVersionNumber {
 public:
     ClangExecutableVersion() : QVersionNumber(-1, -1, -1) {}