move dlfcn-util into basic

I'm going to dlopen_many_sym_or_warn() in src/basic/compress.c, this
will introduce a circular dependency because libshared already depends
from libbasic.
To avoid this, move dlfcn-util.c from libshared to libbasic.

src/basic/meson.build

@@ -21,6 +21,7 @@ basic_sources = files(
         'confidential-virt.c',
         'devnum-util.c',
         'dirent-util.c',
+        'dlfcn-util.c',
         'efivars.c',
         'env-file.c',
         'env-util.c',

src/shared/meson.build

@@ -55,7 +55,6 @@ shared_sources = files(
         'device-nodes.c',
         'discover-image.c',
         'dissect-image.c',
-        'dlfcn-util.c',
         'dm-util.c',
         'dns-domain.c',
         'dropin.c',