Enable lld for windows

Bug: http://b/110800681

The following flags that the binutils linkers support are not available
in lld for Windows:
  -soname
  --no-undefined
  -rpath

Windows also uses "import libraries", which are stub libraries used only
for linking.  The binutils linkers accepted a DLL and treated them as an
import library.  But lld issues the following error:

  lld-link: error: ...DLL: bad file type. Did you specify a DLL instead
  of an import library?

To resolve this, pass '-out-implib=libFoo.a' to lld when linking
libFoo.dll.  Add libFoo.a as an implicit output to the 'ld' build rule.

Rewrite the shared libraries for a library/binary to use the import
library instead of the DLL.  As a side-effect, this also (correctly)
uses the AdbWinApi.a that's alongside
development/host/windows/prebuilt/usb/AdbWinApi.dll

Test: Run Windows tests (go/android-llvm-windows-testing) and check
absence of regressions.

Change-Id: I15a178589aa6882caa6e7e38650cc6ef48109764
diff --git a/cc/linker.go b/cc/linker.go
index fd958ba..179a998 100644
--- a/cc/linker.go
+++ b/cc/linker.go
@@ -290,10 +290,6 @@
 	if ctx.Darwin() {
 		return false
 	}
-	// http://b/110800681 - lld cannot link Android's Windows modules yet.
-	if ctx.Windows() {
-		return false
-	}
 	if linker.Properties.Use_clang_lld != nil {
 		return Bool(linker.Properties.Use_clang_lld)
 	}
@@ -347,7 +343,7 @@
 			// darwin defaults to treating undefined symbols as errors
 			flags.LdFlags = append(flags.LdFlags, "-Wl,-undefined,dynamic_lookup")
 		}
-	} else if !ctx.Darwin() {
+	} else if !ctx.Darwin() && !ctx.Windows() {
 		flags.LdFlags = append(flags.LdFlags, "-Wl,--no-undefined")
 	}
 
@@ -384,7 +380,7 @@
 
 	flags.LdFlags = append(flags.LdFlags, proptools.NinjaAndShellEscapeList(linker.Properties.Ldflags)...)
 
-	if ctx.Host() {
+	if ctx.Host() && !ctx.Windows() {
 		rpath_prefix := `\$$ORIGIN/`
 		if ctx.Darwin() {
 			rpath_prefix = "@loader_path/"