RFR: 8338916: Build warnings about overriding recipe for jvm-ldflags.txt

[Magnus Ihse Bursie]

>From the bug report:

Users are reporting warnings like this:

lib/CompileGtest.gmk:84: warning: overriding recipe for target '/.../build/linux-x64/make-support/compile-commands/jvm-ldflags.txt'
lib/CompileJvm.gmk:166: warning: ignoring old recipe for target '/.../build/linux-x64/make-support/compile-commands/jvm-ldflags.txt'

I believe this is caused by [JDK-8338290](https://bugs.openjdk.org/browse/JDK-8338290), where the jvm-ldflags.txt target file isn't made unique enough.

-------------

Commit messages:
 - 8338916: Build warnings about overriding recipe for jvm-ldflags.txt

Changes: https://git.openjdk.org/jdk/pull/20819/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20819&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338916
  Stats: 2 lines in 2 files changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20819.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20819/head:pull/20819

PR: https://git.openjdk.org/jdk/pull/20819