Add tests for unused attribute in multi-name declarations

The unused attribute in declarations with several names now marks the
correct variable or struct member.

Author: Anton Lindqvist

test/testunusedvar.cpp

@@ -2068,6 +2068,11 @@ class TestUnusedVar : public TestFixture {
                                "    int i3 __attribute__((unused)) {};\n"
                                "};\n");
         ASSERT_EQUALS("", errout_str());
+
+        checkStructMemberUsage("struct S {\n"
+                               "    int a __attribute__((unused)), b;\n"
+                               "};\n");
+        ASSERT_EQUALS("[test.cpp:2:36]: (style) struct member 'S::b' is never used. [unusedStructMember]\n", errout_str());
     }
 
     void structmember31() { // #14130
@@ -6015,6 +6020,12 @@ class TestUnusedVar : public TestFixture {
                               "    char b[1][2] __attribute__((unused));\n"
                               "}\n");
         ASSERT_EQUALS("", errout_str());
+
+        functionVariableUsage("int foo()\n"
+                              "{\n"
+                              "    int x __attribute__((unused)), y;\n"
+                              "}\n");
+        ASSERT_EQUALS("[test.cpp:3:36]: (style) Unused variable: y [unusedVariable]\n", errout_str());
     }
 
     void localvarFunction() {