BUILD.bazel

* Build boot_stage2 with Bazel

Introduces the initial foundations of a Bazel build, including a
toolchain, critical generated headers, platform patterns, and enough
BUILD files to build boot_stage2.

* Bazel libraries to support picotool

* Move SDK defines to toolchain

* Switch to `archive_override` in MODULE.bazel

Uses archive_override where applicable to allow transitive bzlmod deps
to propagate.

* Multiplatform objcopy selection in Bazel build

Makes an objcopy alias that redirects to the objcopy tool for the
current exec platform, which allows boot_stage2 to build on Linux,
macOS, and Windows.

* Generate Bazel build files

Adds initial set of generated Bazel build files. Note that these do not
yet build, as dependency cycles are present.

* Fix dependency cycles in Bazel build

Fixes many dependency cycles, some were unintentionally created by the
build file generator, others are true dependency cycles that require
manual workarounds.

* Silence warning in pico_stdio Bazel build

Silences a stray warning in the Bazel build.

* Fix wildcard Bazel build

This makes `bazel build //...` succeed, and also prevents the fetching
of toolchains that aren't compatible with the current execution
environment (i.e. Windows computers will no longer try to download macOS
toolchains).

* Get the SDK working

Finishes out the remainder of the work required to successfully compile
a working blinky example.

* Fix UART stdio dependencies in Bazel build

Fixes some dependencies around pico_stdlib so that pico_stdlib links
properly and UART stdio works.

* Add linux support to Bazel build

* Get Bazel deps from registry

Adds external an external registry for resolving Bazel module
dependencies.

* Fix host configuration for picotool

Provides the appropriate defines for host builds to support the picotool
build.

* Remove -ffreestanding from Bazel toolchain

The -ffreestanding toolchain flag is quite strict, so remove it from the
Bazel toolchain.

* Remove unused .bzl file

* Reduce Bazel compiler flags

Cuts out most of the Bazel toolchain flags and only specifies the
bare-minimum set of flags. Also, adds wrapper linker flags for functions
the SDK wraps.

* Get USB serial working

Adds initial TinyUSB support and enough integration to get USB serial
working.

* Remove "Generated build file"

Removes comments that indicates BUILD.bazel files are generated. This
was used during initial bringup to indicate hand-crafted vs
automatically generated BUILD.bazel files.

* Do not build USB libraries unless configured

Prevents USB libraries from being built unless the build is properly
configured to use them.

* Switch to rules_cc toolchains

Moves toolchain configuration to use the new rules in rules_cc.

* Minor cleanup in parse_version.py

Cleans up trailing whitespace and runs the black formatter on
parse_version.py.

* Simplify constraint dimensions in Bazel build

Consolidates the class/chip constraint settings to be a single
constraint_setting with a config_setting that represents the rp2 class.

* Update pin of rules_cc in Bazel build

Includes a necessary fix for the target_compatible_with expression in
the cc_toolchain to work as intended.

* Move toolchains from pico.bzl to BUILD.bazel

Moves toolchain definitions from pico.bzl to BUILD.bazel to make them
easier to find and read.

* Run buildifier on Bazel build files

Fix trivial formatting issues by running buildifier on all BUILD.bazel
files.

* Make objcopy rule

Makes a simple objcopy rule to remove direct references to the ARM
toolchains.

* Fix link flags in Bazel build

Critical flags were not being applied to link steps. This applies -mcpu
and -mthumb to the link steps to make the produced binaries work again.

* Mention missing host build support

* Fix various Bazel library rules

* pico_bit_ops was incomplete.
* pico_double and pico_float were trying to link in the "none"
  implementation.

* Extend Bazel build documentation

Improves documentation and comments across the Bazel build.

* Clean up auxilary tools in Bazel build

Switches genrules to use skylib rules to simplify things. Reworks
version header generation to use the Bazel module version rather than
parsing CMake.

* Update boot_stage2 Bazel build file

Moves `includes` to be enumerated on the correct library.

* Add WORKSPACE version fallback

WORKSPACE Bazel projects don't support querying module version, so add a
fallback of '0.0.1-WORKSPACE' so the build can succeed.

* Fix malloc handling in Bazel build

* Fix Bazel dependency cycle in pico_malloc

* Prevent malloc from being linked into boot_stage2

Prevents Bazel from ever trying to link malloc into the boot_stage2
binary.

* Remove custom bootloader platform

A dedicated boot_stage2 platform introduces a lot of complexity that
needs to be more thought-through.