RFR: 8301697: [s390] Optimized-build is broken [v2]

[Amit Kumar]

> This fix guards `__ asm_assert_eq("killed Z_R14", 0)` & `__asm_assert_mem8_is_zero(in_bytes(JavaThread::exception_pc_offset()), Z_thread, "exception pc already set : "FILE_AND_LINE, 0)` with ASSERT because on s390x  `JavaThread::exception_oop_offset()` is always cleared but `JavaThread::exception_pc_offset()` is being cleared only in ASSERT-def, Which is causing the build failure in Optimized-Debug.

Amit Kumar has updated the pull request incrementally with two additional commits since the last revision:

 - Merge branch 'optimized_build_broken' of github.com:offamitkumar/jdk into optimized_build_broken
 - addressing comments from lutz and tyler

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12400/files
  - new: https://git.openjdk.org/jdk/pull/12400/files/6455f9db..fae3bf91

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12400&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12400&range=00-01

  Stats: 19 lines in 3 files changed: 1 ins; 7 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/12400.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12400/head:pull/12400

PR: https://git.openjdk.org/jdk/pull/12400