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

[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.

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Commit messages:
 - Merge branch 'master' into optimized_build_broken
 - guards asserts statements
 - fixes optimized build

Changes: https://git.openjdk.org/jdk/pull/12400/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12400&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301697
  Stats: 9 lines in 2 files changed: 3 ins; 0 del; 6 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