glsl: Kill __intrinsic_atomic_sub

Just generate an __intrinsic_atomic_add with a negated parameter.

Some background on the non-obvious reasons for the the big change to
builtin_builder::call()... this is cribbed from some discussion with
Ilia on mesa-dev.

Why change builtin_builder::call() to allow taking dereferences and
create them here rather than just feeding in the ir_variables directly?
The problem is the neg_data ir_variable node would have to be in two
lists at the same time: the instruction stream and parameters.  The
ir_variable node is automatically added to the instruction stream by the
call to make_temp.  Restructuring the code so that the ir_variables
could be in parameters then move them to the instruction stream would
have been pretty terrible.

ir_call in the instruction stream has an exec_list that contains
ir_dereference_variable nodes.

The builtin_builder::call method previously took an exec_list of
ir_variables and created a list of ir_dereference_variable.  All of the
original users of that method wanted to make a function call using
exactly the set of parameters passed to the built-in function (i.e.,
call __intrinsic_atomic_add using the parameters to atomicAdd).  For
these users, the list of ir_variables already existed:  the list of
parameters in the built-in function signature.

This new caller doesn't do that.  It wants to call a function with a
parameter from the function and a value calculated in the function.  So,
I changed builtin_builder::call to take a list that could either be a
list of ir_variable or a list of ir_dereference_variable.  In the former
case it behaves just as it previously did.  In the latter case, it uses
(and removes from the input list) the ir_dereference_variable nodes
instead of creating new ones.

   text	   data	    bss	    dec	    hex	filename
6036395	 283160	  28608	6348163	 60dd83	lib64/i965_dri.so before
6036923	 283160	  28608	6348691	 60df93	lib64/i965_dri.so after

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Acked-by: Ilia Mirkin <imirkin@alum.mit.edu>

src/compiler/glsl/ir.h

@@ -1045,7 +1045,6 @@ enum ir_intrinsic_id {
    ir_intrinsic_atomic_counter_increment,
    ir_intrinsic_atomic_counter_predecrement,
    ir_intrinsic_atomic_counter_add,
-   ir_intrinsic_atomic_counter_sub,
    ir_intrinsic_atomic_counter_and,
    ir_intrinsic_atomic_counter_or,
    ir_intrinsic_atomic_counter_xor,