Rewrite fsverity_init in C++ and load keys from keystore

Test: still see keys loaded from /product appears in /proc/keys
Test: Add X.509 DER cert files to keystore, see the key in
      /proc/keys after reboot
Bug: 112038744
Change-Id: I08006d8befa69e4bf416a2bed9e1813725877147
diff --git a/fsverity_init/Android.bp b/fsverity_init/Android.bp
new file mode 100644
index 0000000..407849d
--- /dev/null
+++ b/fsverity_init/Android.bp
@@ -0,0 +1,18 @@
+cc_binary {
+    name: "fsverity_init",
+    srcs: [
+        "fsverity_init.cpp",
+    ],
+    static_libs: [
+        "libc++fs",
+        "libmini_keyctl_static",
+    ],
+    shared_libs: [
+        "libbase",
+        "libkeystore_binder",
+        "libkeyutils",
+        "liblog",
+        "liblogwrap",
+    ],
+    cflags: ["-Werror", "-Wall", "-Wextra"],
+}