gn build: Port r342002

[thakis]

Summary

I had hoped we could remove the dependency on shell32.lib from lib/Support (there isn't much depending on it), but looks like this will take a while. So for now, port this over.

[rnk]

lgtm

llvm/trunk/utils/gn/secondary/llvm/lib/Support/BUILD.gn

sources = [
     "VirtualFileSystem.cpp",
     "Watchdog.cpp",
   ]
 
   libs = []
 
   if (current_os == "linux" || current_os == "android") {
     libs += [ "dl" ]
+  } else if (current_os == "win") {
+    # Delay load shell32.dll if possible to speed up process startup.
+    libs += [ "delayimp.lib" ]
+    ldflags = [
+      "-delayload:ole32.dll",
+      "-delayload:shell32.dll",
+    ]
   }
 }