Add semantic check for precision qualifier on wrong kind of type. Added a few more tests.

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@22170 e7fa87d3-cd2b-0410-9028-fcbf551c1848

Test/precision.frag

@@ -68,3 +68,9 @@ void main()
     texture2D(samplerMed, vec2(0.1, 0.2));
     texture2D(samplerHigh, vec2(0.1, 0.2));
 }
+
+precision mediump bool;                 // ERROR
+//precision mediump struct { int a; } s;  // ERROR
+struct s {int a;};
+precision mediump s;                    // ERROR
+mediump bvec2 b2;                       // ERROR