fix: dev: Make libcap mandatory on Linux again

When refactoring the BIND 9.21 build system to meson, libcap was
unintentionally made optional on Linux.

Closes #5590

Merge branch '5590-make-libcap-mandatory-on-linux-again' into 'main'

See merge request isc-projects/bind9!11136

meson.build

@@ -50,7 +50,6 @@ meson_lto = get_option('b_lto')
 trace_logging = get_option('trace-logging')
 rcu_flavor = get_option('rcu-flavor')
 
-cap_opt = get_option('cap')
 cmocka_opt = get_option('cmocka')
 dnstap_opt = get_option('dnstap')
 doc_opt = get_option('doc')
@@ -818,11 +817,9 @@ endif
 
 ## libcap
 cap_dep = null_dep
-if cap_opt.allowed()
-    cap_dep = dependency('libcap', required: cap_opt)
-    if cap_dep.found()
-        config.set('HAVE_LIBCAP', 1)
-    endif
+cap_dep = dependency('libcap', required: host_machine.system() == 'linux')
+if cap_dep.found()
+    config.set('HAVE_LIBCAP', 1)
 endif
 
 ## IDN

meson_options.txt

@@ -17,13 +17,6 @@ option(
     description: 'Enable sphinx-based documentation generation',
 )
 
-option(
-    'cap',
-    type: 'feature',
-    value: 'auto',
-    description: 'Enable libcap-based capability support',
-)
-
 option(
     'dnstap',
     type: 'feature',