[android] Migrate Android toolchain rules to use llvm-{nm|strip}.

Bug: 877080
Change-Id: Ib0797ee0cac35b62925f45ad87ff5a7a48385618
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2770538
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#865912}

build/toolchain/android/BUILD.gn

@@ -55,9 +55,8 @@ template("android_clang_toolchain") {
     ar = "$_prefix/llvm-ar"
     ld = cxx
     readelf = _tool_prefix + "readelf"
-    nm = _tool_prefix + "nm"
-    strip = rebase_path("//buildtools/third_party/eu-strip/bin/eu-strip",
-                        root_build_dir)
+    nm = "$_prefix/llvm-nm"
+    strip = "$_prefix/llvm-strip"
     if (_use_debug_fission) {
       dwp = _tool_prefix + "dwp"
     }