bpo-42246: Don't eliminate jumps to jump, if it will break PEP 626.

[markshannon]

Consider the following weird function:

deff(x):
whileTrue:
ifx:
breakcontinue

On master this produces the code:

 1 >> 0 NOP
2 2 LOAD_FAST 0 (x)
4 POP_JUMP_IF_FALSE 0
3 6 LOAD_CONST 0 (None)
8 RETURN_VALUE

which, when x is False will generate the trace 1, 2, 1, 2, 1, 2, ...

with this PR it produces the following correct, if slightly less efficient code:

 1 >> 0 NOP
2 2 LOAD_FAST 0 (x)
4 POP_JUMP_IF_FALSE 10
3 6 LOAD_CONST 0 (None)
8 RETURN_VALUE
4 >> 10 JUMP_ABSOLUTE 0

which generates the correct trace 1, 2, 4, 1, 2, 4, 1, 2, 4, ...

When https://bugs.python.org/issue42719 is addressed we should be able to produce more efficient code.

https://bugs.python.org/issue42246