CLang flags query:: I'm wanting to port software to FreeBSD

[Joe Nosay]

I've noticed different flags such as -Wno-parentheses and such along with
the -Wno-unused-variable. I would like to know where would be a good source
online to find the flags; and, I would like to know what flags are used by
porters to optimize builds. These will be placed on the Makefile of the
source such that it can be built  natively on FreeBSD. I would be able to
test software.
Thanks