Switch platform EH unwinder to prebuilt LLVM libunwind

For the platform libc++ STL, remove the
-Wl,--exclude-libs,libunwind_llvm.a argument, which is redundant with
the same argument in deviceGlobalLdflags.

Bug: http://b/153025717
Test: device boots
Change-Id: Idd7791d52f74aab2d5f59419fb75f841fc29a2eb

cc/stl.go

@@ -140,11 +140,7 @@ func needsLibAndroidSupport(ctx BaseModuleContext) bool {
 }
 
 func staticUnwinder(ctx android.BaseModuleContext) string {
-	if ctx.Arch().ArchType == android.Arm {
-		return "libunwind_llvm"
-	} else {
-		return "libgcc_stripped"
-	}
+	return "libunwind"
 }
 
 func (stl *stl) deps(ctx BaseModuleContext, deps Deps) Deps {
@@ -192,6 +188,7 @@ func (stl *stl) deps(ctx BaseModuleContext, deps Deps) Deps {
 		if needsLibAndroidSupport(ctx) {
 			deps.StaticLibs = append(deps.StaticLibs, "ndk_libandroid_support")
 		}
+		// TODO: Switch the NDK over to the LLVM unwinder for non-arm32 architectures.
 		if ctx.Arch().ArchType == android.Arm {
 			deps.StaticLibs = append(deps.StaticLibs, "ndk_libunwind")
 		} else {
@@ -231,10 +228,6 @@ func (stl *stl) flags(ctx ModuleContext, flags Flags) Flags {
 					// Use Win32 threads in libc++.
 					"-D_LIBCPP_HAS_THREAD_API_WIN32")
 			}
-		} else {
-			if ctx.Arch().ArchType == android.Arm {
-				flags.Local.LdFlags = append(flags.Local.LdFlags, "-Wl,--exclude-libs,libunwind_llvm.a")
-			}
 		}
 	case "libstdc++":
 		// Nothing