RFR: 8196896: Use SYSROOT_CFLAGS in dtrace gensrc

[Magnus Ihse Bursie]

We are missing `$(SYSROOT_CFLAGS)` when calling `$(CPP)` directly (instead of going via `SetupNativeCompilation`).

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Commit messages:
 - 8196896: Use SYSROOT_CFLAGS in dtrace gensrc

Changes: https://git.openjdk.org/jdk/pull/24160/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24160&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8196896
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/24160.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24160/head:pull/24160

PR: https://git.openjdk.org/jdk/pull/24160