win: Pass /libpath: on Windows too, and use /lldignoreenv to make lld ignore the %LIB% env var.

See https://reviews.llvm.org/D67456

Makes the build a bit more hermetic, and should have no behavior change.

Bug: none
Change-Id: I90080aa7f8ec814e6ec9b1a4fbcad464e12a450d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1807154
Auto-Submit: Nico Weber <thakis@chromium.org>
Commit-Queue: Reid Kleckner <rnk@chromium.org>
Reviewed-by: Reid Kleckner <rnk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697369}

build/config/win/BUILD.gn

@@ -142,6 +142,9 @@ config("compiler") {
     # (link.exe also writes the current time, but it doesn't have a flag to
     # override that behavior.)
     ldflags += [ "/TIMESTAMP:" + build_timestamp ]
+
+    # Don't look for libpaths in %LIB%, similar to /X in cflags above.
+    ldflags += [ "/lldignoreenv" ]
   }
 
   if (!is_debug && !is_component_build) {

build/toolchain/win/BUILD.gn

@@ -130,17 +130,17 @@ template("msvc_toolchain") {
 
     # ninja does not have -t msvc other than windows, and lld doesn't depend on
     # mt.exe in PATH on non-Windows, so it's not needed there anyways.
-    if (defined(invoker.sys_lib_flags)) {
+    if (host_os != "win") {
       linker_wrapper = ""
       sys_lib_flags = "${invoker.sys_lib_flags} "  # Note trailing space
-    } else if (use_lld) {
+    } else if (defined(invoker.sys_lib_flags)) {
       # Invoke ninja as wrapper instead of tool wrapper, because python
       # invocation requires higher cpu usage compared to ninja invocation, and
       # the python wrapper is only needed to work around link.exe problems.
       # TODO(thakis): Remove wrapper once lld-link can merge manifests without
       # relying on mt.exe being in %PATH% on Windows, https://crbug.com/872740
       linker_wrapper = "ninja -t msvc -e $env -- "  # Note trailing space.
-      sys_lib_flags = ""
+      sys_lib_flags = "${invoker.sys_lib_flags} "  # Note trailing space
     } else {
       linker_wrapper =
           "$python_path $tool_wrapper_path link-wrapper $env False "  # Note trailing space.
@@ -359,10 +359,6 @@ template("win_toolchains") {
   msvc_toolchain(target_name) {
     environment = "environment." + toolchain_arch
     cl = "${goma_prefix}\"${win_toolchain_data.vc_bin_dir}/cl.exe\""
-    if (host_os != "win") {
-      # For win cross build
-      sys_lib_flags = "${win_toolchain_data.libpath_flags}"
-    }
 
     toolchain_args = {
       if (defined(invoker.toolchain_args)) {
@@ -383,10 +379,7 @@ template("win_toolchains") {
       cl = string_replace(cl, "/", "\\")
     }
     sys_include_flags = "${win_toolchain_data.include_flags_imsvc}"
-    if (host_os != "win") {
-      # For win cross build
-      sys_lib_flags = "${win_toolchain_data.libpath_flags}"
-    }
+    sys_lib_flags = "${win_toolchain_data.libpath_flags}"
 
     toolchain_args = {
       if (defined(invoker.toolchain_args)) {