glsl: Free all S-Expressions immediately after reading IR.
glsl: Free all S-Expressions immediately after reading IR.

For some reason I thought subexpressions were chained off the top-level
one.  This isn't the case, so just create a temporary context and free
it.  All of this memory would be eventually freed, but now is freed
much sooner.

Signed-off-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>

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