RFR: 8315020: The macro definition for LoongArch64 zero build is not accurate.

[Ao Qi]

The `LOONGARCH` is not a macro that must be defined. It is not a C/C++ pre-defined macro and is also not pre-defined in libraries such as libffi. We'd better use a macro defined in jdk.

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Commit messages:
 - 8315020: The macro definition for LoongArch64 zero build is not accurate.

Changes: https://git.openjdk.org/jdk/pull/15428/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15428&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315020
  Stats: 3 lines in 2 files changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15428.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15428/head:pull/15428

PR: https://git.openjdk.org/jdk/pull/15428