Put Throwable.getMessage behind a boundary in posix builtins

Author: zapster

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/PosixModuleBuiltins.java

@@ -1838,7 +1838,7 @@ String readlink(String str, @SuppressWarnings("unused") PNone none) {
             try {
                 return getContext().getEnv().getTruffleFile(str).getCanonicalFile().getPath();
             } catch (IOException e) {
-                throw raise(OSError, e.getMessage());
+                throw raise(OSError, getMessage(e));
             }
         }
     }

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/nodes/PNodeWithContext.java

@@ -117,7 +117,7 @@ public final PException raise(PythonBuiltinClassType type, Exception e) {
     }
 
     @TruffleBoundary
-    private static final String getMessage(Exception e) {
+    protected static final String getMessage(Exception e) {
         return e.getMessage();
     }