Set mixed builds use product-config based target

Rather than specifying a specific arch/os, use the android_target
platform that incorporates arch/os based on product config.

Test: build/bazel/ci/mixed_libc.sh
Change-Id: I2b30cfb9778444acbfd7648af2d331303cab416a
diff --git a/android/bazel_handler.go b/android/bazel_handler.go
index c6364af..341d500 100644
--- a/android/bazel_handler.go
+++ b/android/bazel_handler.go
@@ -333,7 +333,7 @@
 	// The actual platform values here may be overridden by configuration
 	// transitions from the buildroot.
 	cmdFlags = append(cmdFlags,
-		fmt.Sprintf("--platforms=%s", "//build/bazel/platforms:android_arm"))
+		fmt.Sprintf("--platforms=%s", "//build/bazel/platforms:android_target"))
 	cmdFlags = append(cmdFlags,
 		fmt.Sprintf("--extra_toolchains=%s", "//prebuilts/clang/host/linux-x86:all"))
 	// This should be parameterized on the host OS, but let's restrict to linux