vkd3d-shader/hlsl: Avoid leaking blocks on YYABORT.

Currently program errors might result on instructions that use
ctx->error_instr as src. In case we hit YYABORT while parsing another
part of the HLSL source, we have to make sure that the block that
contains the instruction is properly cleaned up, or we might hit the

    vkd3d:590273:err:hlsl_free_instr Failed assertion: list_empty(&node->uses)

assertion when hlsl_ctx_cleanup() is called after the YYABORT.

Consider the following shader:

    float4 main() : sv_target
    {
        // Statement A
        int p = foo;      // initializer argument is ERROR.
        // Statement B
        undeclared_fun(); // triggers YYABORT.
    }

Statement A will src the ctx->error_instr because of the undeclared
identifier and Statement B will trigger an YYABORT because of the
undeclared function.

libs/vkd3d-shader/hlsl.y

@@ -6768,6 +6768,7 @@ static void validate_uav_type(struct hlsl_ctx *ctx, enum hlsl_sampler_dim dim,
 %type <block> statement_list
 %type <block> switch_statement
 %type <block> unary_expr
+%destructor { destroy_block($$); } <block>
 
 %type <boolval> boolean