Improve simplifyJumps to rewrite

  IFEQ L4
  L5
  GOTO L6

to

  IFNE L6
  L5

This rewrite is only correct if L5 is not the target of any jump
instruction (otherwise, removing the GOTO would change semantics).
Previously we did not do the rewrite if there was any label between
the conditional jump and the goto (like L5). Now we track which labels
are jump targets.

Rewrite tests for new optimizer
  - SI-6941
  - SI-2171
  - t3430
  - t3252
  - t4840
  - t2171
  - t3430
  - t3252
  - t6157
  - t6547
  - t8062
  - t8306
  - t8359
  - t9123
  - trait-force-info
  - private-inline

test cases for bugs fixed in the new optimizer
  - SI-9160, the unnecessary boxing mentioned in the ticket is optimzied
    since push-pop elimination (scala#4858).
  - SI-8796
  - SI-8524
  - SI-7807

fix flags file for t3420

remove an empty flags file

remove unnecessary partest filters

explicit inliner warnings in test t7582

Restore the lisp test. Removing the flags file - our build runs with the
(new) optimizer enabled anyway.

The test spent the past few years as an optimizer test in pos/
see https://issues.scala-lang.org/browse/SI-4512. The attempt may fail,
but why not give it a try.

$ git lg -S"lisp"

...
| * | | | f785785 - SI-4579 Yoke the power of lisp.scala as a stress for the optimizer. (3 years, 8 months ago) <Jason Zaugg>
...
* | | | | | | 622cc99 - Revert the lisp test. (3 years, 10 months ago) <Paul Phillips>
...
* | | | | | | 97f0324 - Revived the lisp test. (3 years, 10 months ago) <Paul Phillips>
...
* | 1e0f7dc - Imprison the lisp test, no review. (4 years, 4 months ago) <Paul Phillips>
...
* | 6b09630 - "Freed the lisp test." Tweaked partest defaults... (4 years, 6 months ago) <Paul Phillips>
...
* | fec42c1 - Lisp test wins again, no review. (4 years, 8 months ago) <Paul Phillips>
...
* | 1c2d44d - Restored the lisp.scala test. (4 years, 8 months ago) <Paul Phillips>
...
* | 15ed892 - Temporarily sending lisp.scala to be interprete... (4 years, 8 months ago) <Paul Phillips>
...