chromeos: Make the ld path args properly default to the cxx path args.

This should be practically a no-op change since we specify *_ld
explicitly in both the ebuild and in Simple Chrome (for now). But
it will make `gn args --list` print more accurate info wrt these args.

Bug: 937821
Change-Id: I155fd8e2fd6a6275522c768ea96c78eb397a7a7c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2014127Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: George Burgess <gbiv@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734680}

build/toolchain/cros/BUILD.gn

@@ -38,11 +38,8 @@ cros_toolchain("target") {
   ar = cros_target_ar
   cc = cros_target_cc
   cxx = cros_target_cxx
+  ld = cros_target_ld
 
-  ld = cxx
-  if (cros_target_ld != "") {
-    ld = cros_target_ld
-  }
   if (cros_target_nm != "") {
     nm = cros_target_nm
   }
@@ -74,11 +71,8 @@ cros_toolchain("nacl_bootstrap") {
   ar = cros_target_ar
   cc = cros_target_cc
   cxx = cros_target_cxx
+  ld = cros_target_ld
 
-  ld = cxx
-  if (cros_target_ld != "") {
-    ld = cros_target_ld
-  }
   if (cros_target_nm != "") {
     nm = cros_target_nm
   }
@@ -107,11 +101,8 @@ cros_toolchain("host") {
   ar = cros_host_ar
   cc = cros_host_cc
   cxx = cros_host_cxx
+  ld = cros_host_ld
 
-  ld = cxx
-  if (cros_host_ld != "") {
-    ld = cros_host_ld
-  }
   if (cros_host_nm != "") {
     nm = cros_host_nm
   }
@@ -138,11 +129,8 @@ cros_toolchain("v8_snapshot") {
   ar = cros_v8_snapshot_ar
   cc = cros_v8_snapshot_cc
   cxx = cros_v8_snapshot_cxx
+  ld = cros_v8_snapshot_ld
 
-  ld = cxx
-  if (cros_v8_snapshot_ld != "") {
-    ld = cros_v8_snapshot_ld
-  }
   if (cros_v8_snapshot_nm != "") {
     nm = cros_v8_snapshot_nm
   }

build/toolchain/cros_toolchain.gni

@@ -39,7 +39,6 @@ declare_args() {
   cros_target_ar = "ar"
   cros_target_cc = "gcc"
   cros_target_cxx = "g++"
-  cros_target_ld = ""
   cros_target_nm = ""
   cros_target_readelf = ""
 
@@ -55,7 +54,6 @@ declare_args() {
   cros_host_cc = "${clang_base_path}/bin/clang"
   cros_host_cxx = "${clang_base_path}/bin/clang++"
   cros_host_is_clang = true
-  cros_host_ld = ""
   cros_host_nm = ""
   cros_host_readelf = ""
   cros_host_extra_cflags = ""
@@ -67,7 +65,6 @@ declare_args() {
   cros_v8_snapshot_cc = "${clang_base_path}/bin/clang"
   cros_v8_snapshot_cxx = "${clang_base_path}/bin/clang++"
   cros_v8_snapshot_is_clang = true
-  cros_v8_snapshot_ld = ""
   cros_v8_snapshot_nm = ""
   cros_v8_snapshot_readelf = ""
   cros_v8_snapshot_extra_cflags = ""
@@ -80,3 +77,9 @@ declare_args() {
   cros_nacl_bootstrap_extra_cxxflags = ""
   cros_nacl_bootstrap_extra_ldflags = ""
 }
+
+declare_args() {
+  cros_target_ld = cros_target_cxx
+  cros_host_ld = cros_host_cxx
+  cros_v8_snapshot_ld = cros_v8_snapshot_cxx
+}