glsl2: Add and use new variable mode ir_var_temporary

This is quite a large patch because breaking it into smaller pieces
would result in the tree being intermitently broken.  The big changes
are:

    * Add the ir_var_temporary variable mode

    * Change the ir_variable constructor to take the mode as a
      parameter and correctly specify the mode for all ir_varables.

    * Change the linker to not cross validate ir_var_temporary
      variables.

    * Change the linker to pull all ir_var_temporary variables from
      global scope into 'main'.
diff --git a/src/glsl/ast_function.cpp b/src/glsl/ast_function.cpp
index 643eb22..14c36af 100644
--- a/src/glsl/ast_function.cpp
+++ b/src/glsl/ast_function.cpp
@@ -115,7 +115,8 @@
 
 	 var = new(ctx) ir_variable(sig->return_type,
 				    talloc_asprintf(ctx, "%s_retval",
-						    sig->function_name()));
+						    sig->function_name()),
+				    ir_var_temporary);
 	 instructions->push_tail(var);
 
 	 deref = new(ctx) ir_dereference_variable(var);
@@ -509,7 +510,8 @@
    assert(!parameters->is_empty());
 
    ir_variable *var = new(ctx) ir_variable(type,
-					   talloc_strdup(ctx, "vec_ctor"));
+					   talloc_strdup(ctx, "vec_ctor"),
+					   ir_var_temporary);
    instructions->push_tail(var);
 
    /* There are two kinds of vector constructors.
@@ -621,7 +623,8 @@
    assert(!parameters->is_empty());
 
    ir_variable *var = new(ctx) ir_variable(type,
-					   talloc_strdup(ctx, "mat_ctor"));
+					   talloc_strdup(ctx, "mat_ctor"),
+					   ir_var_temporary);
    instructions->push_tail(var);
 
    /* There are three kinds of matrix constructors.
@@ -645,7 +648,8 @@
        */
       ir_variable *rhs_var =
 	 new(ctx) ir_variable(glsl_type::vec4_type,
-			      talloc_strdup(ctx, "mat_ctor_vec"));
+			      talloc_strdup(ctx, "mat_ctor_vec"),
+			      ir_var_temporary);
       instructions->push_tail(rhs_var);
 
       ir_constant_data zero;
@@ -759,7 +763,8 @@
        */
       ir_variable *const rhs_var =
 	 new(ctx) ir_variable(first_param->type,
-			      talloc_strdup(ctx, "mat_ctor_mat"));
+			      talloc_strdup(ctx, "mat_ctor_mat"),
+			      ir_var_temporary);
       instructions->push_tail(rhs_var);
 
       ir_dereference *const rhs_var_ref =
@@ -825,7 +830,8 @@
 	  */
 	 ir_variable *rhs_var =
 	    new(ctx) ir_variable(rhs->type,
-				 talloc_strdup(ctx, "mat_ctor_vec"));
+				 talloc_strdup(ctx, "mat_ctor_vec"),
+				 ir_var_temporary);
 	 instructions->push_tail(rhs_var);
 
 	 ir_dereference *rhs_var_ref =
@@ -1036,7 +1042,8 @@
 	       continue;
 
 	    /* Create a temporary containing the matrix. */
-	    ir_variable *var = new(ctx) ir_variable(matrix->type, "matrix_tmp");
+	    ir_variable *var = new(ctx) ir_variable(matrix->type, "matrix_tmp",
+						    ir_var_temporary);
 	    instructions->push_tail(var);
 	    instructions->push_tail(new(ctx) ir_assignment(new(ctx)
 	       ir_dereference_variable(var), matrix, NULL));