Add support for WebAssembly CPUs and OSes for configure_xcompile

[allsey87]

As discussed in this #1247 (comment) this PR adds support for the WebAssembly CPUs and OSes.

[allsey87]

@novas0x2a any idea why we are getting these errors in CI?

(14:25:43) ERROR: /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/90e2e9b2d72fa9b00c19ff0535bb31ae/external/platforms/os/BUILD: no such target '@@platforms//os:emscripten': target 'emscripten' not declared in package 'os' defined by /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/90e2e9b2d72fa9b00c19ff0535bb31ae/external/platforms/os/BUILD
(14:25:43) ERROR: /workdir/examples/ninja_simple/BUILD.bazel:4:6: every rule of type ninja implicitly depends upon the target '@@platforms//os:emscripten', but this target could not be found because of: no such target '@@platforms//os:emscripten': target 'emscripten' not declared in package 'os' defined by /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/90e2e9b2d72fa9b00c19ff0535bb31ae/external/platforms/os/BUILD

The CPU and OS that I added are defined from platforms 0.0.9 onwards and I have updated the platforms dependency in 924f9c8. Is there something else that needs to be updated, perhaps a lockfile of some sort?

[jsharpe]

@novas0x2a any idea why we are getting these errors in CI?

(14:25:43) ERROR: /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/90e2e9b2d72fa9b00c19ff0535bb31ae/external/platforms/os/BUILD: no such target '@@platforms//os:emscripten': target 'emscripten' not declared in package 'os' defined by /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/90e2e9b2d72fa9b00c19ff0535bb31ae/external/platforms/os/BUILD
(14:25:43) ERROR: /workdir/examples/ninja_simple/BUILD.bazel:4:6: every rule of type ninja implicitly depends upon the target '@@platforms//os:emscripten', but this target could not be found because of: no such target '@@platforms//os:emscripten': target 'emscripten' not declared in package 'os' defined by /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/90e2e9b2d72fa9b00c19ff0535bb31ae/external/platforms/os/BUILD

The CPU and OS that I added are defined from platforms 0.0.9 onwards and I have updated the platforms dependency in 924f9c8. Is there something else that needs to be updated, perhaps a lockfile of some sort?

Its probably the non-bzlmod code path - we don't explicitly depend on platforms at the moment which I guess is a bug; you probably need to add platforms to the workspace macro in rules_foreign_cc/repositories.bzl too?

[allsey87]

Its probably the non-bzlmod code path - we don't explicitly depend on platforms at the moment which I guess is a bug; you probably need to add platforms to the workspace macro in rules_foreign_cc/repositories.bzl too?

Ok, let's handle that in #1263 since it is mostly unrelated to the changes here.