[antlir][oss] fix distro toolchain on oss (#274)

Summary:
Pull Request resolved: #274

The default code for this in the prelude
https://www.internalfb.com/code/fbsource/[d9e5d887126868e28dd50b8911721d351f73a38a]/fbcode/buck2/prelude/cxx/cxx_toolchain_macro_layer.bzl?lines=13-19
https://github.com/facebook/buck2/blob/main/prelude/cxx/cxx_toolchain_macro_layer.bzl#L13-L19
relies on config settings that do not exist in the opensource prelude

Test Plan: Export to PR

Reviewed By: sergeyfd

Differential Revision: D67799115

antlir/distro/toolchain/cxx/defs.bzl

@@ -67,6 +67,7 @@ def _single_image_cxx_toolchain(
         linker = _layer_tool(name, "clang"),
         linker_flags = ["-fuse-ld=lld"] + _llvm_base_args + _include_sysroot(sysroot, "L"),
         linker_type = "gnu",
+        generate_linker_maps = False, # @oss-enable
         nm = _layer_tool(name, "nm"),
         objcopy_for_shared_library_interface = _layer_tool(name, "objcopy"),
         requires_archives = True,