Flip slashes for lib/link commands on Windows

crrev.com/c/1713826 flipped slashes from / to \ so that clang-cl
commands could be copy/paste run on Windows. While investigating a
recent compiler bug I had the need to copy/paste run linker commands on
Windows and realized that I hadn't flipped those slashes. This change
finishes the job, for lib/link commands, tested with component and
non-component builds of base.


Change-Id: If5570ab3093b42908bebab9944cde82da31a055d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1894094
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711887}

build/toolchain/win/BUILD.gn

@@ -102,8 +102,12 @@ template("msvc_toolchain") {
 
       # lld-link includes a replacement for lib.exe that can produce thin
       # archives and understands bitcode (for lto builds).
-      lib = "$prefix/$lld_link /lib"
       link = "$prefix/$lld_link"
+      if (host_os == "win") {
+        # Flip the slashes so that copy/paste of the commands works.
+        link = string_replace(link, "/", "\\")
+      }
+      lib = "$link /lib"
       if (host_os != "win") {
         # See comment adding --rsp-quoting to $cl above for more information.
         link = "$link --rsp-quoting=posix"