gitignore: Add meson build directories
gitignore: Add meson build directories

Change-Id: I6e480c6f561bba0fb3f654f89d78f21988aca3ba
Signed-off-by: William A. Kennington III <30fff5198f4d10ca1117e5f3ec82f3b4b8900d81@google.com>

openbmc/stdplus,openbmc/stdplus