[gn] Don't pass -fprofile-instr-generate to linker on Windows

Avoids a warning from the linker. The user still has to put the resource
directory on the linker search path, and I can't find a clean way to do
that automatically in gn.

llvm/utils/gn/build/BUILD.gn

@@ -233,8 +233,10 @@ config("compiler_defaults") {
       "-fprofile-instr-generate=" +
           rebase_path("$root_build_dir/profiles/%4m.profraw"),
     ]
+    if (host_os != "win") {
       ldflags += [ "-fprofile-instr-generate" ]
     }
+  }
 
   # Deterministic build setup, see
   # http://blog.llvm.org/2019/11/deterministic-builds-with-clang-and-lld.html