Extended the heuristics for obtaining function symbols.

Signed-off-by: Dimitar Dobrev <dpldobrev@yahoo.com>

src/AST/SymbolContext.cs

@@ -87,22 +87,34 @@ namespace CppSharp.AST
             if (FindLibraryBySymbol(symbol, out lib))
                 return true;
 
+            string alternativeSymbol;
+
             // Check for C symbols with a leading underscore.
-            if (FindLibraryBySymbol("_" + symbol, out lib))
+            alternativeSymbol = "_" + symbol;
+            if (FindLibraryBySymbol(alternativeSymbol, out lib))
+            {
+                symbol = alternativeSymbol;
+                return true;
+            }
+
+            alternativeSymbol = symbol.TrimStart('_');
+            if (FindLibraryBySymbol(alternativeSymbol, out lib))
             {
-                symbol = "_" + symbol;
+                symbol = alternativeSymbol;
                 return true;
             }
 
-            if (FindLibraryBySymbol("_imp_" + symbol, out lib))
+            alternativeSymbol = "_imp_" + symbol;
+            if (FindLibraryBySymbol(alternativeSymbol, out lib))
             {
-                symbol = "_imp_" + symbol;
+                symbol = alternativeSymbol;
                 return true;
             }
 
+            alternativeSymbol = "__imp_" + symbol;
             if (FindLibraryBySymbol("__imp_" + symbol, out lib))
             {
-                symbol = "__imp_" + symbol;
+                symbol = alternativeSymbol;
                 return true;
             }