rules_foreign_cc.patch

diff --git foreign_cc/boost_build.bzl foreign_cc/boost_build.bzl
index d8e489f..2462117 100644
--- foreign_cc/boost_build.bzl
+++ foreign_cc/boost_build.bzl
@@ -15,6 +15,7 @@ def _boost_build_impl(ctx):
         ctx.attr,
         configure_name = "BoostBuild",
         create_configure_script = _create_configure_script,
+        tools_data = [],
     )
     return cc_external_rule_impl(ctx, attrs)
 
diff --git foreign_cc/configure.bzl foreign_cc/configure.bzl
index ddfc379..38eec7d 100644
--- foreign_cc/configure.bzl
+++ foreign_cc/configure.bzl
@@ -98,6 +98,7 @@ def _create_configure_script(configureParameters):
         deps = ctx.attr.deps,
         inputs = inputs,
         env_vars = user_env,
+        env_vars_override = ctx.attr.env_override,
         configure_in_place = ctx.attr.configure_in_place,
         prefix_flag = ctx.attr.prefix_flag,
         autoconf = ctx.attr.autoconf,
diff --git foreign_cc/make.bzl foreign_cc/make.bzl
index fcdd8a5..c7c6862 100644
--- foreign_cc/make.bzl
+++ foreign_cc/make.bzl
@@ -74,6 +74,7 @@ def _create_make_script(configureParameters):
         deps = ctx.attr.deps,
         inputs = inputs,
         env_vars = user_env,
+        env_vars_override = ctx.attr.env_override,
         make_commands = make_commands,
     )
 
diff --git foreign_cc/private/configure_script.bzl foreign_cc/private/configure_script.bzl
index 06c516e..de4f470 100644
--- foreign_cc/private/configure_script.bzl
+++ foreign_cc/private/configure_script.bzl
@@ -14,6 +14,7 @@ def create_configure_script(
         deps,
         inputs,
         env_vars,
+        env_vars_override,
         configure_in_place,
         prefix_flag,
         autoconf,
@@ -70,7 +71,7 @@ def create_configure_script(
 
     script.append("##mkdirs## $$BUILD_TMPDIR$$/$$INSTALL_PREFIX$$")
     script.append("{env_vars} {prefix}\"{configure}\" {prefix_flag}$$BUILD_TMPDIR$$/$$INSTALL_PREFIX$$ {user_options}".format(
-        env_vars = get_make_env_vars(workspace_name, tools, flags, env_vars, deps, inputs),
+        env_vars = get_make_env_vars(workspace_name, tools, flags, env_vars, env_vars_override, deps, inputs),
         prefix = configure_prefix,
         configure = configure_path,
         prefix_flag = prefix_flag,
diff --git foreign_cc/private/framework.bzl foreign_cc/private/framework.bzl
index 9c263c0..56f1ae3 100644
--- foreign_cc/private/framework.bzl
+++ foreign_cc/private/framework.bzl
@@ -108,6 +108,13 @@ CC_EXTERNAL_RULE_ATTRIBUTES = {
             "Variables containing `PATH` (e.g. `PATH`, `LD_LIBRARY_PATH`, `CPATH`) entries will be prepended to the existing variable."
         ),
     ),
+    "env_override": attr.string_list(
+        doc = (
+            "List of keys from the 'env' attribute that should override any values set by the underlying C toolchain."
+        ),
+        mandatory = False,
+        default = [],
+    ),
     "includes": attr.string_list(
         doc = (
             "Optional list of include dirs to be passed to the dependencies of this library. " +
diff --git foreign_cc/private/make_env_vars.bzl foreign_cc/private/make_env_vars.bzl
index b5177c7..e70c974 100644
--- foreign_cc/private/make_env_vars.bzl
+++ foreign_cc/private/make_env_vars.bzl
@@ -9,9 +9,10 @@ def get_make_env_vars(
         tools,
         flags,
         user_vars,
+        user_vars_override,
         deps,
         inputs):
-    vars = _get_make_variables(workspace_name, tools, flags, user_vars)
+    vars = _get_make_variables(workspace_name, tools, flags, user_vars, user_vars_override)
     deps_flags = _define_deps_flags(deps, inputs)
 
     # For cross-compilation.
@@ -94,7 +95,7 @@ _MAKE_TOOLS = {
     # missing: cxx_linker_executable
 }
 
-def _get_make_variables(workspace_name, tools, flags, user_env_vars):
+def _get_make_variables(workspace_name, tools, flags, user_env_vars, user_vars_override):
     vars = {}
 
     for flag in _MAKE_FLAGS:
@@ -106,7 +107,10 @@ def _get_make_variables(workspace_name, tools, flags, user_env_vars):
     for user_var in user_env_vars:
         toolchain_val = vars.get(user_var)
         if toolchain_val:
-            vars[user_var] = toolchain_val + [user_env_vars[user_var]]
+            if user_var in user_vars_override:
+                vars[user_var] = [user_env_vars[user_var]]
+            else:
+                vars[user_var] = toolchain_val + [user_env_vars[user_var]]
 
     tools_dict = {}
     for tool in _MAKE_TOOLS:
diff --git foreign_cc/private/make_script.bzl foreign_cc/private/make_script.bzl
index d86ff60..039b0cf 100644
--- foreign_cc/private/make_script.bzl
+++ foreign_cc/private/make_script.bzl
@@ -9,6 +9,7 @@ def create_make_script(
         flags,
         root,
         env_vars,
+        env_vars_override,
         deps,
         inputs,
         make_commands):
@@ -19,7 +20,7 @@ def create_make_script(
     script.append("##symlink_contents_to_dir## $$EXT_BUILD_ROOT$$/{} $$BUILD_TMPDIR$$ False".format(root))
 
     script.append("##enable_tracing##")
-    configure_vars = get_make_env_vars(workspace_name, tools, flags, env_vars, deps, inputs)
+    configure_vars = get_make_env_vars(workspace_name, tools, flags, env_vars, env_vars_override, deps, inputs)
     script.extend(["{env_vars} {command}".format(
         env_vars = configure_vars,
         command = command,