make some plugins used the shared framework

Change-Id: Ie283a4774564f25e0fde8ca35212f92be786d671
Reviewed-on: https://gerrit.libreoffice.org/75785
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

compilerplugins/clang/plugin.cxx

@@ -686,6 +686,17 @@ bool isSamePathname(StringRef pathname, StringRef other)
         pathname, other, [](StringRef p, StringRef a) { return p == a; });
 }
 
+bool hasCLanguageLinkageType(FunctionDecl const * decl) {
+    assert(decl != nullptr);
+    if (decl->isExternC()) {
+        return true;
+    }
+    if (decl->isInExternCContext()) {
+        return true;
+    }
+    return false;
+}
+
 } // namespace
 
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