LightGBM

[R-package] Suppresses unknown pragma warnings during CRAN build (#3460)

* Modified script to also remove pragma warnings.

This also includes modifying the scope of the pragma removal.
Previously this script only searched inside the ./src/include/LightGMB directory.
This was not inclusive enough to remove the warnings in files shown in the ticket.

* Adds CI test that exits if unknown pragma warnings are present.

* Expanding pragma removal to cpp and hpp files.

* Update .ci/test_r_package.sh

Removing unneeded conditions since this script will only run on Linux and Mac builds anyway.

Co-authored-by: James Lamb <jaylamb20@gmail.com>

* Update .ci/test_r_package.sh

Fixes typo

Co-authored-by: James Lamb <jaylamb20@gmail.com>

* replacing double quotes with single quotes

* Using a more portable find syntax so it works on macOS and Linux

Co-authored-by: James Lamb <jaylamb20@gmail.com>