fix: target_compatible_with other workspaces (#73)

When passing different workspaces to customize the target compatibility,
Label removes the workspace name, rendering the wrong string back into
the BUILD.bazel files.

Signed-off-by: Thulio Ferraz Assis <3149049+f0rmiga@users.noreply.github.com>

toolchain/defs.bzl

@@ -49,7 +49,7 @@ def _gcc_toolchain_impl(rctx):
  ]
 
  target_compatible_with = [
- str(Label(v.format(target_arch = target_arch)))
+ v.format(target_arch = target_arch)
  for v in rctx.attr.target_compatible_with
  ]