RFR: 8371650: Add CMakeLists.txt and compile_commands.json into .gitignore

[Leonid Mesnik]

Some IDE and LSP expect to find these files in the project root.
It convenient to place them in src/hotspot, so idea and vim automatically find the root for hotspot project. 

This fix just add these files and some temporary dirs in my ws into .gitignore. Shouldn't harm anyone.

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Commit messages:
 - updated .gitignore

Changes: https://git.openjdk.org/jdk/pull/28248/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28248&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371650
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28248.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28248/head:pull/28248

PR: https://git.openjdk.org/jdk/pull/28248