[jdk13u-dev] RFR: 8261109: [macOS] Remove disabled warning for JNF in make/autoconf/flags-cflags.m4

[Vladimir Kempik]

Almost clean backport to jdk13u-dev. only different filename for gmk file in jdk13 mde it not apply clean ootb.

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Commit messages:
 - 8261109: [macOS] Remove disabled warning for JNF in make/autoconf/flags-cflags.m4

Changes: https://git.openjdk.java.net/jdk13u-dev/pull/235/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk13u-dev&pr=235&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261109
  Stats: 8 lines in 2 files changed: 0 ins; 8 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk13u-dev/pull/235.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk13u-dev pull/235/head:pull/235

PR: https://git.openjdk.java.net/jdk13u-dev/pull/235