Avoid -Werror=deprecated-declarations with recent Clang trunk

...which first added alternative names to and then deprecated getLocBegin/End

Change-Id: Iaefb8ce259057abfa6cd20f0b63c0ef2949a96b2
Reviewed-on: https://gerrit.libreoffice.org/58820
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

compilerplugins/clang/unusedmethodsremove.cxx

@@ -136,7 +136,7 @@ bool UnusedMethodsRemove::VisitCXXMethodDecl( const CXXMethodDecl* functionDecl
         report(
             DiagnosticsEngine::Warning,
             "Could not remove unused method (" + niceName(functionDecl) + ")",
-            functionDecl->getLocStart())
+            compat::getBeginLoc(functionDecl))
           << functionDecl->getSourceRange();
     }
     return true;