Adds dynamic_library_linkopts to zig_cc_toolchain_config

If specified, the flags in dynamic_library_linkopts are included in
cpp_link_dynamic_library and cpp_link_nodeps_dynamic_library actions.

toolchain/private/cc_toolchains.bzl

@@ -32,6 +32,7 @@ def declare_cc_toolchains(absolute_path, zig_include_root):
             absolute_tool_paths[name] = "%s/%s" % (absolute_path, tool_path)
 
         linkopts = target_config.linkopts
+        dynamic_library_linkopts = target_config.dynamic_library_linkopts
         copts = target_config.copts
         for s in getattr(target_config, "linker_version_scripts", []):
             linkopts = linkopts + ["-Wl,--version-script,%s/%s" % (absolute_path, s)]
@@ -45,6 +46,7 @@ def declare_cc_toolchains(absolute_path, zig_include_root):
             cxx_builtin_include_directories = cxx_builtin_include_directories,
             copts = copts,
             linkopts = linkopts,
+            dynamic_library_linkopts = dynamic_library_linkopts,
             target_cpu = target_config.bazel_target_cpu,
             target_system_name = "unknown",
             target_libc = "unknown",

toolchain/private/defs.bzl

@@ -54,6 +54,7 @@ def _target_darwin(gocpu, zigcpu):
             "libc/include/any-macos-any",
         ],
         linkopts = [],
+        dynamic_library_linkopts = [],
         copts = [],
         bazel_target_cpu = "darwin",
         constraint_values = [
@@ -84,6 +85,7 @@ def _target_linux_gnu(gocpu, zigcpu, glibc_version):
         compiler_extra_includes = ["glibc-hacks/glibchack-fcntl.h"] if fcntl_hack else [],
         linker_version_scripts = ["glibc-hacks/fcntl.map"] if fcntl_hack else [],
         linkopts = ["-lc++", "-lc++abi"],
+        dynamic_library_linkopts = [],
         copts = [],
         bazel_target_cpu = "k8",
         constraint_values = [
@@ -105,6 +107,7 @@ def _target_linux_musl(gocpu, zigcpu):
             "libc/include/{}-linux-any".format(zigcpu),
         ] + (["libc/include/x86-linux-any"] if zigcpu == "x86_64" else []),
         linkopts = ["-s", "-w"],
+        dynamic_library_linkopts = [],
         copts = ["-D_LIBCPP_HAS_MUSL_LIBC", "-D_LIBCPP_HAS_THREAD_API_PTHREAD"],
         bazel_target_cpu = "k8",
         constraint_values = [

toolchain/zig_toolchain.bzl

@@ -14,6 +14,11 @@ all_link_actions = [
     ACTION_NAMES.cpp_link_nodeps_dynamic_library,
 ]
 
+dynamic_library_link_actions = [
+    ACTION_NAMES.cpp_link_dynamic_library,
+    ACTION_NAMES.cpp_link_nodeps_dynamic_library,
+]
+
 compile_and_link_actions = [
     ACTION_NAMES.c_compile,
     ACTION_NAMES.cpp_compile,
@@ -73,21 +78,31 @@ def _zig_cc_toolchain_config_impl(ctx):
         ],
     )
 
+    if ctx.attr.dynamic_library_linkopts:
+        dynamic_library_flag_sets = [
+            flag_set(
+                actions = dynamic_library_link_actions,
+                flag_groups = [flag_group(flags = ctx.attr.dynamic_library_linkopts)],
+            ),
+        ]
+    else:
+        dynamic_library_flag_sets = []
+
     default_linker_flags = feature(
         name = "default_linker_flags",
         enabled = True,
         flag_sets = [
             flag_set(
                 actions = all_link_actions,
-                flag_groups = ([
+                flag_groups = [
                     flag_group(
                         flags = ["-target", ctx.attr.target] +
                                 no_gc_sections +
                                 ctx.attr.linkopts,
                     ),
-                ]),
+                ],
             ),
-        ],
+        ] + dynamic_library_flag_sets,
     )
 
     features = [
@@ -119,6 +134,7 @@ zig_cc_toolchain_config = rule(
     attrs = {
         "cxx_builtin_include_directories": attr.string_list(),
         "linkopts": attr.string_list(),
+        "dynamic_library_linkopts": attr.string_list(),
         "copts": attr.string_list(),
         "tool_paths": attr.string_dict(),
         "target": attr.string(),