Manage win lld-link.exe thin archive flag with config("thin_archive")

config/compiler/BUILD.gn

@@ -1676,8 +1676,9 @@ config("export_dynamic") {
 
 # thin_archive -----------------------------------------------------------------
 #
-# Enables thin archives on posix.  Regular archives directly include the object
-# files used to generate it.  Thin archives merely reference the object files.
+# Enables thin archives on posix, and on windows when the lld linker is used.
+# Regular archives directly include the object files used to generate it.
+# Thin archives merely reference the object files.
 # This makes building them faster since it requires less disk IO, but is
 # inappropriate if you wish to redistribute your static library.
 # This config is added to the global config, so thin archives should already be
@@ -1693,6 +1694,8 @@ config("thin_archive") {
   # archive names to 16 characters, which is not what we want).
   if ((is_posix && !is_nacl && !is_mac && !is_ios) || is_fuchsia) {
     arflags = [ "-T" ]
+  } else if (is_win && use_lld) {
+    arflags = [ "/llvmlibthin" ]
   }
 }
 

toolchain/win/BUILD.gn

@@ -116,7 +116,7 @@ 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 /llvmlibthin"
+      lib = "$prefix/$lld_link /lib"
       link = "$prefix/$lld_link"
       if (host_os != "win") {
         # See comment adding --rsp-quoting to $cl above for more information.