Flag guard to make fsverity_init a no-op

As early as fsverity_init, the flag can only be static (thus
is_fixed_read_only). It is now a constant/false and will be flipped
during the ramp up at build time.

Bug: 290064770
Test: mma
Test: Inspect the generated code
Change-Id: I4bd1addb996705f6e6b9f75313bf22b9ecd3e11c
diff --git a/fsverity_init/Android.bp b/fsverity_init/Android.bp
index 07eaf6a..d9bff3b 100644
--- a/fsverity_init/Android.bp
+++ b/fsverity_init/Android.bp
@@ -13,6 +13,7 @@
         "fsverity_init.cpp",
     ],
     static_libs: [
+        "aconfig_fsverity_init_c_lib",
         "libc++fs",
         "libmini_keyctl_static",
     ],
@@ -23,3 +24,14 @@
     ],
     cflags: ["-Werror", "-Wall", "-Wextra"],
 }
+
+aconfig_declarations {
+    name: "aconfig_fsverity_init",
+    package: "android.security.flag",
+    srcs: ["flags.aconfig"],
+}
+
+cc_aconfig_library {
+    name: "aconfig_fsverity_init_c_lib",
+    aconfig_declarations: "aconfig_fsverity_init",
+}