Bazel compiler flags with tests

[martin4861]

Previously compile options have been added to copts by the macros cc_library. Those compile options are meant for compilers like clang or gcc. This tight coupling of macros and compile options makes it impossible to implement any other compiler toolchains, which do not use gcc's or clang's compile options.

To overcome this problem this tight coupling needs to be relaxed. In order to do so, we use Bazel's features. A feature is implemented as follows:

swift_rtti_feature = feature(
    name = "rtti_feature",
    flag_sets = [
        flag_set(
            actions = [ACTION_NAMES.cpp_compile],
            flag_groups = [flag_group(flags = ["-frtti"])],
        ),
    ],
)

Different toolchains might have different compile options for features and are using the abstraction layer using feature.

The features can be simplify activated using cc_library(..., features = ["rtti_feature"], ...). The activation is handled by the macros in defs2.bzl.

This PR consists of multiple changes:

• toolchains now implement the features for compile option selection by the macros.
• the new macros in defs2.bzl support the selection of features, whereas the legacy macros in defs.bzl stay unchanged.
• defs2.bzl provides new macros, which set different levels of features, depending on the needed coding quality level (see the extensive doc in defs2.bzl.)