gitignore: compile_commands.json is only top-level

Change-Id: I313b86d8736e948d52d57bad77550f2969c9fc67
Reviewed-on: https://gerrit.libreoffice.org/39107
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Muhammet Kara <muhammet.kara@pardus.org.tr>
diff --git a/.gitignore b/.gitignore
index 3ec069d..e31e480 100644
--- a/.gitignore
+++ b/.gitignore
@@ -173,4 +173,4 @@ LibreOffice.VC.VC.opendb
*.sublime-workspace

# vim-ide-integration
compile_commands.json
/compile_commands.json