[GN] Add solink_module tool on the Mac, Win, and GCC toolchains.

build/toolchain/mac/BUILD.gn

Index: build/toolchain/mac/BUILD.gn
diff --git a/build/toolchain/mac/BUILD.gn b/build/toolchain/mac/BUILD.gn
index 5d918d0038288004eb336d0cdf52d02c21b4bc9c..3f6ffc2400bd0dfb6f8e427a5c8e25aa00d0ecf9 100644
--- a/build/toolchain/mac/BUILD.gn
+++ b/build/toolchain/mac/BUILD.gn
@@ -167,6 +167,33 @@ template("mac_toolchain") {
       depend_output = tocname
     }
 
+    tool("solink_module") {
+      sofile = "{{root_out_dir}}/{{target_output_name}}{{output_extension}}"  # eg "./libfoo.so"
+      rspfile = sofile + ".rsp"
+
+      link_command = "$ld -bundle {{ldflags}} -o $sofile -Wl,-filelist,$rspfile"
+      if (is_component_build) {
+        link_command += " -Wl,-install_name,@rpath/{{target_output_name}}{{output_extension}}"
+      }
+      link_command += " {{solibs}} {{libs}}"
+      command = link_command
+
+      rspfile_content = "{{inputs_newline}}"
+
+      description = "SOLINK_MODULE {{output}}"
+
+      # Use this for {{output_extension}} expansions unless a target manually
+      # overrides it (in which case {{output_extension}} will be what the target
+      # specifies).
+      default_output_extension = ".so"
+
+      output_prefix = "lib"
+
+      outputs = [
+        sofile,
+      ]
+    }
+
     tool("link") {
       outfile = "{{root_out_dir}}/{{target_output_name}}{{output_extension}}"
       rspfile = "$outfile.rsp"