Fixed false positives about strdupa() / strndupa() memleak

strdupa() / strndupa() allocates memory on the stack using alloca().
This memory is freed automatically once the current function is left.

cfg/posix.cfg

@@ -26,6 +26,7 @@
     </arg>
   </function>
   <function name="strdupa">
+    <use-retval/>
     <noreturn>false</noreturn>
     <arg nr="1">
       <not-null/>
@@ -43,6 +44,7 @@
     </arg>
   </function>
   <function name="strndupa">
+    <use-retval/>
     <noreturn>false</noreturn>
     <arg nr="1">
       <not-null/>
@@ -342,8 +344,6 @@
     <dealloc>free</dealloc>
     <alloc init="true">strdup</alloc>
     <alloc init="true">strndup</alloc>
-    <alloc init="true">strdupa</alloc>
-    <alloc init="true">strndupa</alloc>
     <alloc init="true">wcsdup</alloc>
   </memory>
   <resource>

test/testmemleak.cpp

@@ -4277,6 +4277,13 @@ private:
               "}", &settings);
         ASSERT_EQUALS("[test.cpp:3]: (error) Resource leak: f\n", errout.str());
 
+        // strdupa allocates on the stack, no free() needed
+        check("void x()\n"
+              "{\n"
+              "    char *s = strdupa(\"Test\");\n"
+              "}", &settings);
+        ASSERT_EQUALS("", errout.str());
+
         LOAD_LIB_2(settings.library, "gtk.cfg");
 
         check("void f(char *a) {\n"

test/testother.cpp

@@ -172,6 +172,7 @@ private:
         TEST_CASE(integerOverflow); // #5895
 
         TEST_CASE(testReturnIgnoredReturnValue);
+        TEST_CASE(testReturnIgnoredReturnValuePosix);
     }
 
     void check(const char code[], const char *filename = nullptr, bool experimental = false, bool inconclusive = true, bool posix = false, bool runSimpleChecks=true, Settings* settings = 0) {
@@ -6366,6 +6367,23 @@ private:
               "}");
         ASSERT_EQUALS("", errout.str());
     }
+
+    void testReturnIgnoredReturnValuePosix() {
+        Settings settings_posix;
+        LOAD_LIB_2(settings_posix.library, "posix.cfg");
+
+        check("void f() {\n"
+              "    strdupa(\"test\");\n"
+              "}",
+              "test.cpp",
+              false, // experimental
+              false, // inconclusive
+              true,  // posix
+              false, // runSimpleChecks
+              &settings_posix
+             );
+        ASSERT_EQUALS("[test.cpp:2]: (warning) Return value of function strdupa() is not used.\n", errout.str());
+    }
 };
 
 REGISTER_TEST(TestOther)