dlfcn-util: add static asserts ensuring our sym_xyz() func ptrs match the types from the official headers

Make sure that the sym_xyz function pointers have the types that the
functions we'll assign them have.

And of course, this found a number of incompatibilities right-away, in
particular in the bpf hookup.

(Doing this will trigger deprecation warnings from libbpf. I simply
turned them off locally now, since we are well aware of what we are
doing in that regard.)

There's one return type fix (bool → int), that actually matters I think,
as it might have created an incompatibility on some archs.

src/shared/cryptsetup-util.c

@@ -205,6 +205,14 @@ int dlopen_cryptsetup(void) {
 #if HAVE_LIBCRYPTSETUP
         int r;
 
+        /* libcryptsetup added crypt_reencrypt() in 2.2.0, and marked it obsolete in 2.4.0, replacing it with
+         * crypt_reencrypt_run(), which takes one extra argument but is otherwise identical. The old call is
+         * still available though, and given we want to support 2.2.0 for a while longer, we'll stick to the
+         * old symbol. Howerver, the old symbols now has a GCC deprecation decorator, hence let's turn off
+         * warnings about this for now. */
+
+        DISABLE_WARNING_DEPRECATED_DECLARATIONS;
+
         r = dlopen_many_sym_or_warn(
                         &cryptsetup_dl, "libcryptsetup.so.12", LOG_DEBUG,
                         DLSYM_ARG(crypt_activate_by_passphrase),
@@ -262,6 +270,8 @@ int dlopen_cryptsetup(void) {
         if (r <= 0)
                 return r;
 
+        REENABLE_WARNING;
+
         /* Redirect the default logging calls of libcryptsetup to our own logging infra. (Note that
          * libcryptsetup also maintains per-"struct crypt_device" log functions, which we'll also set
          * whenever allocating a "struct crypt_device" context. Why set both? To be defensive: maybe some