[jdk11u-dev] RFR: 8217233: Update build settings for AIX/xlc

[Tyler Steele]

Discovered while bringing xlc 16.1 support to jdk11. This change adds stack protection to AIX and cleans up the flags to apply #998.

Reviewed-by: clanger, sgroeger

Backport Conflicts:
- minor conflict in flags-cflags.m4 (potentially caused by comment
addition?)

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Commit messages:
 - 8217233: Update build settings for AIX/xlc

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/1030/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=1030&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8217233
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/1030.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/1030/head:pull/1030

PR: https://git.openjdk.java.net/jdk11u-dev/pull/1030