fib in test-jit runs

1. grow/shrink frame size in the pro/epilogue. Note: though we removed
push/pop for unused callee saved registers, we still reserve frame space
for them. Because we generate spill on frame before we know exactly how
large a space is. The solution is to make spill locations patchable.
2. control flow will combine branches in switch instruction if they all
target the same destination.
8 jobs from master in 13 minutes and 43 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #514
test:cargo:api

01:42

passed #516
test:cargo:compiler

01:47

passed #515
test:cargo:ir

01:42

passed #517
test:cargo:runtime

02:36

passed #519
testjit:binops

01:40

failed #520
testjit:cmpops

01:27

failed #521
testjit:convops

01:19

failed #518
testjit:milestones

01:26