RFR: JDK-8313244: NM flags handling in configure process [v3]

[Andreas Steiner]

> On AIX we need the -X64 option for NM in the build. The handling is equivalent to the other used tools flags like AR.
> This change will replace the quick fix done in https://bugs.openjdk.org/browse/JDK-8312466.

Andreas Steiner has updated the pull request incrementally with one additional commit since the last revision:

  add missing NMFLAGS to nm calls on other target OS too, improve comment

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15150/files
  - new: https://git.openjdk.org/jdk/pull/15150/files/6752fc12..1addaede

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15150&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15150&range=01-02

  Stats: 4 lines in 3 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/15150.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15150/head:pull/15150

PR: https://git.openjdk.org/jdk/pull/15150