Pass -undefined dynamic_lookup to dynamic library linking actions on Mac

This change fixes a bug introduced in 2d0e27e. Before, we allowed dynamic libraries to have undefined symbols on mac, but after that change this stopped working.

Fixes #7607.

RELNOTES: None.
PiperOrigin-RevId: 238644308

src/test/shell/bazel/cc_integration_test.sh

@@ -103,4 +103,52 @@ EOF
   bazel build :ok || fail "Should have found include at synthetic path"
 }
 
+# This test tests that Bazel can produce dynamic libraries that have undefined
+# symbols on Mac and Linux. Not sure it is a sane default to allow undefined
+# symbols, but it's the default we had historically. This test creates
+# an executable (main) that defines bar(), and a shared library (plugin) that
+# calls bar(). When linking the libplugin.so, symbol 'bar' is undefined.
+#    +-----------------------------+     +----------------------------------+
+#    |  main                       |     |  libplugin.so                    |
+#    |                             |     |                                  |
+#    |   main() { return foo(); } +---------> foo() { return bar() - 42; }  |
+#    |                             |     |       +                          |
+#    |                             |     |       |                          |
+#    |   bar() { return 42; } <------------------+                          |
+#    |                             |     |                                  |
+#    +-----------------------------+     +----------------------------------+
+function test_undefined_dynamic_lookup() {
+  if is_windows; then
+    # Windows doesn't allow undefined symbols in shared libraries.
+    return 0
+  fi
+  mkdir -p "dynamic_lookup"
+  cat > "dynamic_lookup/BUILD" <<EOF
+cc_binary(
+  name = "libplugin.so",
+  srcs = ["plugin.cc"],
+  linkshared = 1,
+)
+
+cc_binary(
+    name = "main",
+    srcs = ["main.cc", "libplugin.so"],
+)
+EOF
+
+  cat > "dynamic_lookup/plugin.cc" <<EOF
+int bar();
+int foo() { return bar() - 42; }
+EOF
+
+  cat > "dynamic_lookup/main.cc" <<EOF
+int foo();
+int bar() { return 42; }
+int main() { return foo(); }
+EOF
+
+  bazel build //dynamic_lookup:main || fail "Bazel couldn't build the binary."
+  bazel run //dynamic_lookup:main || fail "Run of the binary failed."
+}
+
 run_suite "cc_integration_test"

tools/osx/crosstool/cc_toolchain_config.bzl.tpl

@@ -3517,13 +3517,15 @@ def _impl(ctx):
                     ],
                 ),
                 flag_set(
-                    actions = [ACTION_NAMES.cpp_link_nodeps_dynamic_library],
+                    actions = [
+                      ACTION_NAMES.cpp_link_dynamic_library,
+                      ACTION_NAMES.cpp_link_nodeps_dynamic_library,
+                    ],
                     flag_groups = [flag_group(flags = ["-undefined", "dynamic_lookup"])],
                 ),
                 flag_set(
                     actions = [
                         ACTION_NAMES.cpp_link_executable,
-                        ACTION_NAMES.cpp_link_dynamic_library,
                         "objc-executable",
                         "objc++-executable",
                     ],