glsl: Put a bunch of optimization visitors under anonymous namespaces.

Because these classes are used entirely from their own source files
and not from separate DSOs, the linker gets to produce massively less
code.  This cuts about 13k of text in the libdricore case.  In the
non-libdricore case, the additional linkage information allows the
compiler to inline some code, so libglsl.a size actually increases by
about 300 bytes.

For a dricore build, improves shader_runner runtime on
glsl-fs-copy-propagation-texcoords-1 by 0.21% +/- 0.03% (n=353574,
outliers removed).  No statistically significant difference with n=322
on glslparsertest on a yofrankie shader intended to test compiler
performance.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/opt_dead_code_local.cpp

@@ -40,6 +40,8 @@
 
 static bool debug = false;
 
+namespace {
+
 class assignment_entry : public exec_node
 {
 public:
@@ -138,6 +140,7 @@ public:
    ir_hierarchical_visitor *visitor;
 };
 
+} /* unnamed namespace */
 
 /**
  * Adds an entry to the available copy list if it's a plain assignment