RFR: 8375241: Simplify --with-native-debug-symbols-level option implementation

[Julian Waters]

--with-native-debug-symbols-level was added some time ago to allow selecting the level of debugging information created for compiled binaries. The UTIL_ARG_WITH utility that the option implementation uses has several features that can be used to simplify handling of this option, so that is done in this change.

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Commit messages:
 - Simplify native-debug-symbols-level in flags-cflags.m4

Changes: https://git.openjdk.org/jdk/pull/29214/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29214&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375241
  Stats: 20 lines in 1 file changed: 4 ins; 11 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/29214.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29214/head:pull/29214

PR: https://git.openjdk.org/jdk/pull/29214