Builds using feature fips or fips-link-precompiled now
read variables prefixed by BORING_BSSL_FIPS_ instead of
BORING_BSSL_. This helps complex builds where build dependencies
also use boring, where we may not want to use fips there.
Without those separate variables, the boring build for the
build dependencies end up relying on e.g. BORING_BSSL_PATH,
causing errors if this path is a boring checkout intended for
fips builds, while the fips feature isn't enabled for
the build dependency.
This means BORING_SSL_PRECOMPILED_BCM_O is now
BORING_BSSL_PRECOMPILED_BCM_O.
Prefix BORING_BSSL_ has been chosen because that's the
one that is used the most among all the variables
the build script uses.
Using a struct improves navigation of the build script,
as we can rely on rust-analyzer to help us check how
a feature flag or an environment variable is used,
as opposed to grepping for multiple env::var calls
or #[cfg] attributes.
This commit also removes some obsolete blocks of code
related to the now defunct ndk-old-gcc and fuzzing features.
Anthony Ramine