glsl2: Make sure _mesa_glsl_parse_state constructor gets a context

Fix an major regression in dc754586.  Too bad that change was
obviously never tested.
diff --git a/src/glsl/builtin_function.cpp b/src/glsl/builtin_function.cpp
index 4a319ef..d96c15c 100644
--- a/src/glsl/builtin_function.cpp
+++ b/src/glsl/builtin_function.cpp
@@ -35,9 +35,10 @@
 gl_shader *
 read_builtins(GLenum target, const char *protos, const char **functions, unsigned count)
 {
+   GLcontext fakeCtx;
    gl_shader *sh = _mesa_new_shader(NULL, 0, target);
    struct _mesa_glsl_parse_state *st =
-      new(sh) _mesa_glsl_parse_state(NULL, target, sh);
+      new(sh) _mesa_glsl_parse_state(&fakeCtx, target, sh);
 
    st->language_version = 130;
    st->symbols->language_version = 130;