This change configures the Linux clang -Og target as a toolchain with
args. To support this, all Pigweed variables from pw_vars_default are
made into build args, defined within their respective modules.
The Linux clang target/toolchain is the only one that currently works.
Pigweed's other targets will be ported in later changes.
Change-Id: I051e29fde7577e41a3184c37031a4e04936404e1
Require targets to explicitly import pigweed variable definitions. This
moves out some necessary logic from the BUILDCONFIG.gn file.
Change-Id: If9c9fe5a680cc9d897a0e8a55889873be618ed84
This change replaces the implicit overrides of the default GN target
types in BUILDCONFIG.gn with explicit pw_* versions. This is done to
allow Pigweed to build within larger GN projects without modifying their
BUILDCONFIG files.
Change-Id: I1d1e41d5e9bde8fe076f7031f3c2b98b9630ff70
