glsl_symbol_table: Add new talloc-based new()

We take advantage of overloading of the new operator (with an
additional parameter!) to make this look as "C++ like" as possible.

This closes 507 memory leaks when compiling glsl-orangebook-ch06-bump.frag
when measured with:

	valgrind ./glsl glsl-orangebook-ch06-bump.frag

as seen here:

	total heap usage: 55,623 allocs, 14,389 frees
	(was 13,882 frees before)

1 files changed, 4 insertions, 0 deletions

diff --git a/ir.h b/ir.h
index 9277f76..68e9065 100644
--- a/ir.h
+++ b/ir.h
@@ -29,6 +29,10 @@
 #include <cstdio>
 #include <cstdlib>
 
+extern "C" {
+#include <talloc.h>
+}
+
 #include "list.h"
 #include "ir_visitor.h"
 #include "ir_hierarchical_visitor.h"