fix for Clang 3.8 warning in SkSL

src/sksl/SkSLParser.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
  
 #include "stdio.h"
 #include "SkSLParser.h"
 #include "SkSLToken.h"
 
 #define register
 #ifdef __clang__
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wunneeded-internal-declaration"
+#pragma clang diagnostic ignored "-Wnull-conversion"
 #endif
 #include "lex.sksl.c"
 #ifdef __clang__
 #pragma clang diagnostic pop
 #endif
 #undef register
 
 #include "ast/SkSLASTBinaryExpression.h"
 #include "ast/SkSLASTBlock.h"
 #include "ast/SkSLASTBoolLiteral.h"
@@ skipping 1355 matching lines @@
 bool Parser::identifier(std::string* dest) {
     Token t;
     if (this->expect(Token::IDENTIFIER, "identifier", &t)) {
         *dest = t.fText; 
         return true;
     }
     return false;
 }
 
 } // namespace