Add exporting compile_commands.json file

* Add an option in scons script to export compile_commands.json
  file to support development using language server.
* Add .cache directory to the git ignore list. It is normally
  used by clangd as the local cache.

Resolves: COMPMID-5940
Signed-off-by: Viet-Hoa Do <viet-hoa.do@arm.com>
Change-Id: I8c2a1ac85942d34ada22adea3e7de2baf2189eb2
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/9258
Benchmark: Arm Jenkins <bsgcomp@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Jakub Sujak <jakub.sujak@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
diff --git a/.gitignore b/.gitignore
index 6852bdd..ac38812 100644
--- a/.gitignore
+++ b/.gitignore
@@ -52,3 +52,4 @@
 # IDE folders
 .idea/
 .vscode/
+.cache/