Add ability to treat keywords as identifiers in versions that had not yet reserved the keyword.

Test/120.frag

 #version 120
 
-lowp vec3 a;
-mediump float b;
-highp int c;
+float lowp;
+float mediump;
+float highp;
 
-precision highp float;
+float precision;
 
 in vec4 i;
 out vec4 o;

Test/specExamples.frag

@@ -6,11 +6,11 @@ int  a = 0xffffffff;  // 32 bits, a gets the value -1
 //int  b = 0xffffffffU; // ERROR: can't convert uint to int
 uint c = 0xffffffff;  // 32 bits, c gets the value 0xFFFFFFFF
 //uint d = 0xffffffffU; // 32 bits, d gets the value 0xFFFFFFFF
-int  e = -1;          // the literal is “1”, then negation is performed,
+int  e = -1;          // the literal is "1", then negation is performed,
                       //   and the resulting non-literal 32-bit signed 
                       //   bit pattern of 0xFFFFFFFF is assigned, giving e 
                       //   the value of -1.
-//uint f = -1u;         // the literal is “1u”, then negation is performed,
+//uint f = -1u;         // the literal is "1u", then negation is performed,
                       //   and the resulting non-literal 32-bit unsigned 
                       //   bit pattern of 0xFFFFFFFF is assigned, giving f 
                       //   the value of 0xFFFFFFFF.

glslang/MachineIndependent/glslang.y

@@ -73,6 +73,7 @@ Jutta Degener, 1995
 #endif
 
 %}
+
 %union {
     struct {
         TSourceLoc line;
@@ -1664,6 +1665,7 @@ storage_qualifier
 
         parseContext.checkDeprecated($1.line, ENoProfile, 140, "attribute");
         parseContext.requireNotRemoved($1.line, ECoreProfile, 420, "attribute");
+        parseContext.requireNotRemoved($1.line, EEsProfile, 300, "attribute");
 
         if (parseContext.globalErrorCheck($1.line, parseContext.symbolTable.atGlobalLevel(), "attribute"))
             parseContext.recover();
@@ -1674,6 +1676,7 @@ storage_qualifier
     | VARYING {
         parseContext.checkDeprecated($1.line, ENoProfile, 140, "varying");
         parseContext.requireNotRemoved($1.line, ECoreProfile, 420, "varying");
+        parseContext.requireNotRemoved($1.line, EEsProfile, 300, "varying");
         
         if (parseContext.globalErrorCheck($1.line, parseContext.symbolTable.atGlobalLevel(), "varying"))
             parseContext.recover();