meson: make sure we never actually link to libxenctrl

We don't make use of any of its symbols, we just want the headers, hence
make sure we never try to link against it.

meson.build

@@ -1203,6 +1203,7 @@ libxenctrl = dependency('xencontrol',
                         version : '>= 4.9',
                         required : get_option('xenctrl'))
 conf.set10('HAVE_XENCTRL', libxenctrl.found())
+libxenctrl_cflags = libxenctrl.partial_dependency(includes: true, compile_args: true)
 
 feature = get_option('pam')
 libpam = dependency('pam',

src/shared/meson.build

@@ -326,7 +326,7 @@ libshared_deps = [threads,
                   librt,
                   libseccomp,
                   libselinux,
-                  libxenctrl,
+                  libxenctrl_cflags,
                   libxz,
                   libzstd]