Remove Makevars support

There is not enough customization to warrant keeping it in this repo
where it is untested, does not fit well with multiple target toolchains,
and does not have a clear use case.

Author: Siddhartha Bagaria

toolchain/BUILD.toolchain.tpl

@@ -17,8 +17,6 @@ package(default_visibility = ["//visibility:public"])
 load("@rules_cc//cc:defs.bzl", "cc_toolchain", "cc_toolchain_suite")
 load("%{cc_toolchain_config_bzl}", "cc_toolchain_config")
 
-exports_files(["Makevars"])
-
 # Following filegroup targets are used when not using absolute paths and shared
 # between different toolchains.
 

toolchain/Makevars.tpl

@@ -129,7 +129,6 @@ def cc_toolchain_config(
     link_libs = []
 
     # Linker flags:
-    # Keep this logic in sync with _makevars_ld_flags.
     if host_os == "darwin" and not is_xcompile:
         # lld is experimental for Mach-O, so we use the native ld64 linker.
         use_lld = False

toolchain/cc_toolchain_config.bzl

@@ -30,15 +30,6 @@ load(
 )
 load("@rules_cc//cc:defs.bzl", _cc_toolchain = "cc_toolchain")
 
-def _makevars_ld_flags(rctx, os):
-    # Keep this logic in sync with cc_toolchain_config.
-
-    if os == "darwin":
-        return ""
-
-    # lld, as of LLVM 7, is experimental for Mach-O, so we use it only on linux.
-    return "-fuse-ld=lld"
-
 def _include_dirs_str(rctx, key):
     dirs = rctx.attr.cxx_builtin_include_directories.get(key)
     if not dirs:
@@ -154,16 +145,6 @@ def llvm_register_toolchains():
         },
     )
 
-    # Make vars useful for languages that interface with C/C++ and use the 'make' system.
-    rctx.template(
-        "Makevars",
-        Label("//toolchain:Makevars.tpl"),
-        {
-            "%{toolchain_path_prefix}": toolchain_path_prefix,
-            "%{makevars_ld_flags}": _makevars_ld_flags(rctx, os),
-        },
-    )
-
 def _cc_toolchains_str(workspace_name, toolchain_info, use_absolute_paths):
     # Since all the toolchains rely on downloading the right LLVM toolchain for
     # the host architecture, we don't need to explicitly specify