tree-wide: drop gcrypt dependency from all binaries except for unit tests

With this change, gcrypt dependency is not mandatory. Hence, allow to build
systemd even when -D gcrypt=enabled but gcrypt devel package is not installed.

meson.build

@@ -1206,8 +1206,9 @@ libqrencode = dependency('libqrencode',
 libqrencode_cflags = libqrencode.partial_dependency(includes: true, compile_args: true)
 conf.set10('HAVE_QRENCODE', libqrencode.found())
 
+feature = get_option('gcrypt')
 libgcrypt = dependency('libgcrypt',
-                       required : get_option('gcrypt'))
+                       required : feature.disabled() ? feature : false)
 conf.set10('HAVE_GCRYPT', libgcrypt.found())
 if libgcrypt.found()
         libgcrypt_cflags = libgcrypt.partial_dependency(includes: true, compile_args: true)