glsl: consistently use ifndef guards over pragma once

Through the glsl headers we had an odd mix of guards be that
"ifndef", "pragma once" neither or both.

Simplify things by using the more common ones (ifndef) and annotating
all the sources, barring the generated builting header -
builtin_int64.h.

The final header - udivmod64.h - is [seemingly] unused and on its way
out (patch purge it is on the mailing list).

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Acked-by: Vedran Miletić <vedran@miletic.net>
Acked-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>

src/compiler/glsl/ir_rvalue_visitor.h

@@ -30,6 +30,9 @@
  * a pointer to each rvalue in the tree.
  */
 
+#ifndef GLSL_IR_RVALUE_VISITOR_H
+#define GLSL_IR_RVALUE_VISITOR_H
+
 class ir_rvalue_base_visitor : public ir_hierarchical_visitor {
 public:
    ir_visitor_status rvalue_visit(ir_assignment *);
@@ -81,3 +84,5 @@ public:
    virtual ir_visitor_status visit_enter(ir_emit_vertex *);
    virtual ir_visitor_status visit_enter(ir_end_primitive *);
 };
+
+#endif /* GLSL_IR_RVALUE_VISITOR_H */