added initial GLSL support to skslc

src/sksl/sksl.flex

 /*
 
         This file is IGNORED during the build process!
 
         As this file is updated so infrequently and flex is not universally present on build machines,
         the lex.sksl.c file must be manually regenerated if you make any changes to this file. Just run:
 
                 flex sksl.flex
 
     You will have to manually add a copyright notice to the top of lex.sksl.c.
@@ skipping 50 matching lines @@
 uniform { return SkSL::Token::UNIFORM; }
 
 const { return SkSL::Token::CONST; }
 
 lowp { return SkSL::Token::LOWP; }
 
 mediump { return SkSL::Token::MEDIUMP; }
 
 highp { return SkSL::Token::HIGHP; }
 
+flat { return SkSL::Token::FLAT; }
+
+noperspective { return SkSL::Token::NOPERSPECTIVE; }
+
 struct { return SkSL::Token::STRUCT; }
 
 layout { return SkSL::Token::LAYOUT; }
 
 precision { return SkSL::Token::PRECISION; }
 
 {LETTER}({DIGIT}|{LETTER})* { return SkSL::Token::IDENTIFIER; }
 
 "#"{LETTER}({DIGIT}|{LETTER})* { return SkSL::Token::DIRECTIVE; }
 
@@ skipping 97 matching lines @@
 
 [ \t\r\n]+  /* whitespace */
 
 .    { return SkSL::Token::INVALID_TOKEN; }
 
 %%
 
 int skslwrap(yyscan_t scanner) {
     return 1; // terminate
 }