bugc: list variables before a function's first statement - #358

Two runs of code that bugc emits outside any IR instruction had no variables context, so a debugger listed no variables at all on the steps after them:

• the memory setup at the start of the code (and create) block, which sets the free memory pointer and the frame pointer: only a code range, so the storage variables were missing for the first few steps
• a function's entry JUMPDEST and its prologue, which allocates the frame and stores the arguments in it: an invoke and a code range. The parameters are live here, but they were not listed until the body's first instruction

Both now list the variables of the entry block, as the variables pass gives them just before its first instruction (or that instruction's own, when the function has no locals). A local is listed without a pointer. During the prologue the frame pointer still names the caller's frame until the prologue has set it up, so a frame-relative pointer would read the caller's words. The invoke's arguments already point at the parameters on the stack.

The empty block on a branch edge into a block with phis also listed no variables. #356 fixes that, because the block's missing inline transform had the same cause.