Create intermediate cobalt toolchain for native linker modular builds (…

…#1516)

b/294450490

Make an intermediate cobalt toolchain template which can be used for
native linker modular builds.

(cherry picked from commit e8a8ca6)

starboard/build/config/BUILDCONFIG.gn

@@ -99,7 +99,7 @@ if (target_cpu == "x86" || target_cpu == "arm") {
 host_toolchain = "//starboard/build/toolchain/$host_os:$_host_toolchain_cpu"
 
 if (build_with_separate_cobalt_toolchain) {
-  cobalt_toolchain = "//starboard/build/toolchain:clang"
+  cobalt_toolchain = "//$starboard_path/toolchain:cobalt"
   starboard_toolchain = "//$starboard_path/toolchain:starboard"
 } else {
   cobalt_toolchain = "//$starboard_path/toolchain:target"

starboard/build/toolchain/cobalt_toolchains.gni

@@ -0,0 +1,52 @@
+# Copyright 2023 The Cobalt Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import("//build/config/win/visual_studio_version.gni")
+import("//build/toolchain/gcc_toolchain.gni")
+
+template("cobalt_clang_toolchain") {
+  gcc_toolchain(target_name) {
+    forward_variables_from(invoker.variables,
+                           [
+                             "native_linker_path",
+                             "executable_extension",
+                             "shlib_extension",
+                           ])
+    assert(defined(native_linker_path),
+           "native_linker_path has to be defined by the platform")
+    if (!is_host_win) {
+      prefix = rebase_path("$clang_base_path/bin", root_build_dir)
+      cc = "$prefix/clang"
+      cxx = "$prefix/clang++"
+      ld = native_linker_path
+      readelf = "readelf"
+      ar = "${prefix}/llvm-ar"
+      nm = "nm"
+    } else {
+      prefix = llvm_clang_path
+      cc = "$prefix/clang.exe"
+      cxx = "$prefix/clang++.exe"
+      ld = native_linker_path
+      readelf = "$prefix/llvm-readobj.exe"
+      ar = "${prefix}/llvm-ar.exe"
+      nm = "${prefix}/llvm-nm.exe"
+    }
+    toolchain_args = {
+      if (defined(invoker.toolchain_args)) {
+        forward_variables_from(invoker.toolchain_args, "*")
+      }
+      is_clang = true
+    }
+  }
+}

starboard/linux/x64x11/toolchain/BUILD.gn

@@ -13,12 +13,19 @@
 # limitations under the License.
 
 import("//build/config/clang/clang.gni")
+import("//starboard/build/toolchain/cobalt_toolchains.gni")
 import("//starboard/shared/toolchain/overridable_gcc_toolchain.gni")
 
 overridable_clang_toolchain("starboard") {
   clang_base_path = clang_base_path
 }
 
+cobalt_clang_toolchain("cobalt") {
+  variables = {
+    native_linker_path = "$clang_base_path/bin/clang++"
+  }
+}
+
 overridable_clang_toolchain("target") {
   clang_base_path = clang_base_path
 }

starboard/raspi/2/toolchain/BUILD.gn

@@ -13,8 +13,15 @@
 # limitations under the License.
 
 import("//build/toolchain/gcc_toolchain.gni")
+import("//starboard/build/toolchain/cobalt_toolchains.gni")
 import("//starboard/raspi/shared/toolchain/raspi_shared_toolchain.gni")
 
+cobalt_clang_toolchain("cobalt") {
+  variables = {
+    native_linker_path = gcc_toolchain_cxx
+  }
+}
+
 gcc_toolchain("starboard") {
   cc = gcc_toolchain_cc
   cxx = gcc_toolchain_cxx