Switch everything to platforms

This patch switches the codebase over from using the "cpu"
mechanism to using bazel platforms. See
https://docs.bazel.build/versions/master/platforms.html for some more
information.

Most of the substantial changes are in //tools. Instead of using
`cc_toolchain_suite` rules, we now use regular `toolchain` rules that
are registered in the WORKSPACE. That also means that bazel now uses
the target platform to select the compiler.

All --cpu=* arguments should now be --config=* arguments. For example,
`--cpu=roborio` should now be `--config=roborio`. The CI script and
all documentation has been updated to reflect that.

The remainder of the changes revolve around tagging all targets with
`target_compatible_with`.  The old mechanism allowed us to specify
repo-wide defaults. The new mechanism does not. That means every
target that didn't have any compatibility specified, now requires
compatibility with `@platforms//os:linux`.

I used buildozer for the vast majority of `target_compatible_with`
changes. buildozer automatically buildifies any BUILD files it
touches. That means this patch also contains a few non-functional
changes that I was too lazy to remove.

Change-Id: I66d6e6ad9161520ee397597cdb492585820a3acd
diff --git a/tools/build_rules/BUILD b/tools/build_rules/BUILD
index 8ad7018..cf27ca0 100644
--- a/tools/build_rules/BUILD
+++ b/tools/build_rules/BUILD
@@ -1,12 +1,14 @@
 sh_binary(
     name = "quiet_success",
     srcs = ["quiet_success.sh"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
 )
 
 py_binary(
     name = "jinja2_generator",
     srcs = ["jinja2_generator.py"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = ["@python_jinja2"],
 )
diff --git a/tools/build_rules/fortran.bzl b/tools/build_rules/fortran.bzl
index 9e6e789..d55f1c1 100644
--- a/tools/build_rules/fortran.bzl
+++ b/tools/build_rules/fortran.bzl
@@ -1,109 +1,5 @@
 load("@//tools/build_rules:select.bzl", "compiler_select")
 
-def _single_fortran_object_impl(ctx):
-    toolchain_cflags = (ctx.fragments.cpp.compiler_options([]) +
-                        ctx.fragments.cpp.c_options +
-                        ctx.fragments.cpp.unfiltered_compiler_options([]) +
-                        [
-                            "-fPIC",
-                            "-Wno-maybe-uninitialized",
-                            "-Wno-unused-dummy-argument",
-                            "-Wno-conversion",
-                            "-Wno-unused-variable",
-                            "-Wno-character-truncation",
-                        ])
-
-    cmd = toolchain_cflags + ["-c", ctx.file.src.path, "-o", ctx.outputs.pic_o.path]
-    filtered_cmd = []
-
-    # Strip out the C/C++/Clang specific flags.
-    exclude_flags = [
-        "-fcolor-diagnostics",
-        "-Wswitch-enum",
-        "-Wpointer-arith",
-        "-Wcast-qual",
-        "-Wwrite-strings",
-        "-Wsign-compare",
-        "-Wformat=2",
-        "-Werror",
-        "-Wextra",
-        "-Wno-builtin-macro-redefined",
-        "-Wunused-local-typedefs",
-        "-D__has_feature(x)=0",
-        "-fmacro-backtrace-limit=0",
-    ]
-
-    for flag in cmd:
-        if flag not in exclude_flags and not (flag.startswith("-fsanitize") or
-                                              flag.startswith("-fno-sanitize")):
-            filtered_cmd.append(flag)
-
-    ctx.action(
-        inputs = [ctx.file.src] + ctx.files._cc_toolchain,
-        outputs = [ctx.outputs.pic_o],
-        mnemonic = "Fortran",
-        executable = ctx.fragments.cpp.compiler_executable,
-        arguments = filtered_cmd,
-        progress_message = "Building %s" % ctx.outputs.pic_o.short_path,
-    )
-
-def _define_fortran_output(src):
-    if not src.name.endswith(".f"):
-        fail("Fortran files must end in '.f'", "src")
-
-    fortran_file_base = src.name[:-2]
-    return {
-        "pic_o": fortran_file_base + ".pic.o",
-    }
-
-_single_fortran_object = rule(
-    attrs = {
-        "src": attr.label(
-            allow_single_file = [".f"],
-        ),
-        "cc_libs": attr.label_list(providers = ["cc"]),
-        # TODO(Brian): Replace this with something more fine-grained from the
-        # configuration fragment or something.
-        "_cc_toolchain": attr.label(
-            default = Label("@//tools/cpp:toolchain"),
-        ),
-    },
-    fragments = [
-        "cpp",
-    ],
-    outputs = _define_fortran_output,
-    implementation = _single_fortran_object_impl,
-)
-
-def fortran_library(name, srcs, deps = [], visibility = None):
-    """Builds a shared library from a set of fortran files.
-
-    Args:
-      srcs: list of fortran files ending in .f
-      deps: cc_library or fortran_library dependencies.
-    """
-    pic_o_files = []
-    for src in srcs:
-        pic_o_file = src[:-2] + ".pic.o"
-        _single_fortran_object(
-            name = name + "_" + pic_o_file,
-            src = src,
-            visibility = ["//visibility:private"],
-            restricted_to = ["@//tools:k8"],
-        )
-        pic_o_files.append(pic_o_file)
-
-    native.cc_library(
-        name = name,
-        deps = deps,
-        srcs = pic_o_files,
-        linkopts = [
-            "-lgfortran",
-        ],
-        visibility = visibility,
-        restricted_to = ["@//tools:k8"],
-    )
-
 f2c_copts = compiler_select({
     "clang": [
         "-Wno-incompatible-pointer-types-discards-qualifiers",
diff --git a/tools/build_rules/pandoc.bzl b/tools/build_rules/pandoc.bzl
index bc63bac..ad47ccc 100644
--- a/tools/build_rules/pandoc.bzl
+++ b/tools/build_rules/pandoc.bzl
@@ -6,7 +6,7 @@
   src: Markdown file to convert. Only one file can be specified.
 """
 
-def pandoc_html(name, src):
+def pandoc_html(name, src, target_compatible_with = None):
     output = name + ".html"
     native.genrule(
         name = name,
@@ -15,4 +15,5 @@
         cmd = "$(location @pandoc//:pandoc_wrapper) -s $< -o $@",
         tools = ["@pandoc//:all_files", "@pandoc//:pandoc_wrapper"],
         executable = True,
+        target_compatible_with = target_compatible_with,
     )
diff --git a/tools/build_rules/select.bzl b/tools/build_rules/select.bzl
index 1c48eb7..23addf5 100644
--- a/tools/build_rules/select.bzl
+++ b/tools/build_rules/select.bzl
@@ -46,7 +46,8 @@
         "@//tools:cpu_roborio": values["roborio"],
         "@//tools:cpu_armhf": values["armhf"],
         "@//tools:cpu_cortex_m4f": values["cortex-m"],
-        "@//tools:cpu_cortex_m4f_k22": values["cortex-m"],
+        # TODO(phil): Support this properly.
+        #"@//tools:cpu_cortex_m4f_k22": values["cortex-m"],
     })
 
 """A select wrapper for address space sizes.
@@ -66,7 +67,8 @@
         "@//tools:cpu_roborio": values["32"],
         "@//tools:cpu_armhf": values["32"],
         "@//tools:cpu_cortex_m4f": values["32"],
-        "@//tools:cpu_cortex_m4f_k22": values["32"],
+        # TODO(phil): Support this properly.
+        #"@//tools:cpu_cortex_m4f_k22": values["32"],
     })
 
 """A select wrapper for compilers.