glsl: Never put ir_var_temporary variables in the symbol table

glsl: Never put ir_var_temporary variables in the symbol table

Later patches will give every ir_var_temporary the same name in release
builds.  Adding a bunch of variables named "compiler_temp" to the symbol
table can only cause problems.

No change Valgrind massif results for a trimmed apitrace of dota2.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>