glsl: Hide many classes local to individual .cpp files in anon namespaces.

This gives the compiler the chance to inline and not export class symbols
even in the absence of LTO.  Saves about 60kb on disk.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@.intel.com>

src/glsl/lower_instructions.cpp

@@ -109,6 +109,8 @@
 
 using namespace ir_builder;
 
+namespace {
+
 class lower_instructions_visitor : public ir_hierarchical_visitor {
 public:
    lower_instructions_visitor(unsigned lower)
@@ -133,6 +135,8 @@ private:
    void ldexp_to_arith(ir_expression *);
 };
 
+} /* anonymous namespace */
+
 /**
  * Determine if a particular type of lowering should occur
  */