Modify VA_BLOCK_ARG semantics.
* `MIR_VA_ARG` takes va_list and any memory operand and returns
address of the next argument in the 1st insn operand. The memory
operand type defines the type of the argument
- * `MIR_VA_BLOCK_ARG` takes va_list and integer operand and returns
- address of the next argument passed as a block argument
- of the size given by the integer operand
+ * `MIR_VA_BLOCK_ARG` takes result address, va_list, and integer operand
+ and moves the next argument passed as block of give size to the result address
* va_list operand can be memory with undefined type. In this case
address of the va_list is not in the memory but is the
memory address
