Put GN object files in subdir based on the label.

build/toolchain/win/BUILD.gn

Index: build/toolchain/win/BUILD.gn
diff --git a/build/toolchain/win/BUILD.gn b/build/toolchain/win/BUILD.gn
index 4b550525712c3aadc8510cc327c76da692e387e5..b80ef1d0ec3687cb17b94b9f9659ebe0f2c34885 100644
--- a/build/toolchain/win/BUILD.gn
+++ b/build/toolchain/win/BUILD.gn
@@ -84,6 +84,9 @@ template("msvc_toolchain") {
     lib_switch = ""
     lib_dir_switch = "/LIBPATH:"
 
+    # Object files go in this directory.
+    object_subdir = "{{target_out_dir}}/{{label_name}}"
+
     tool("cc") {
       rspfile = "{{output}}.rsp"
       precompiled_header_type = "msvc"
@@ -92,7 +95,7 @@ template("msvc_toolchain") {
       depsformat = "msvc"
       description = "CC {{output}}"
       outputs = [
-        "{{target_out_dir}}/{{target_output_name}}/{{source_name_part}}.obj",
+        "$object_subdir/{{source_name_part}}.obj",
       ]
       rspfile_content = "{{defines}} {{include_dirs}} {{cflags}} {{cflags_c}}"
     }
@@ -107,7 +110,7 @@ template("msvc_toolchain") {
       depsformat = "msvc"
       description = "CXX {{output}}"
       outputs = [
-        "{{target_out_dir}}/{{target_output_name}}/{{source_name_part}}.obj",
+        "$object_subdir/{{source_name_part}}.obj",
       ]
       rspfile_content = "{{defines}} {{include_dirs}} {{cflags}} {{cflags_cc}}"
     }
@@ -115,7 +118,7 @@ template("msvc_toolchain") {
     tool("rc") {
       command = "$python_path gyp-win-tool rc-wrapper $env rc.exe {{defines}} {{include_dirs}} /fo{{output}} {{source}}"
       outputs = [
-        "{{target_out_dir}}/{{target_output_name}}/{{source_name_part}}.res",
+        "$object_subdir/{{source_name_part}}.res",
       ]
       description = "RC {{output}}"
     }
@@ -129,7 +132,7 @@ template("msvc_toolchain") {
       command = "$python_path gyp-win-tool asm-wrapper $env $ml {{defines}} {{include_dirs}} {{asmflags}} /c /Fo{{output}} {{source}}"
       description = "ASM {{output}}"
       outputs = [
-        "{{target_out_dir}}/{{target_output_name}}/{{source_name_part}}.obj",
+        "$object_subdir/{{source_name_part}}.obj",
       ]
     }