meson: remove false check for key_serial_t

key_serial_t is defined in keyutil.h, which wasn't included in the header list
in the test, so the test always failed. We were always compiling stuff with
!HAVE_KEY_SERIAL_T.

We could try to add keyutil.h to the test, but then we'd have to first check if
it is available, which just doesn't seem worth the trouble.

key_serial_t should always be defined as int32_t. Let's keep the uncoditional
define, since repeated compatible typedefs are not a problem, and it allows us
to compile even if the header file is missing. If there's ever a change in the
definition, we'll have to adjust the code for the different type anyway, and
our compiler will tell us.

meson.build

@@ -423,11 +423,9 @@ decl_headers = '''
 #include <linux/fib_rules.h>
 #include <sys/stat.h>
 '''
-# FIXME: key_serial_t is only defined in keyutils.h, this is bound to fail
 
 foreach decl : ['char16_t',
                 'char32_t',
-                'key_serial_t',
                 'struct ethtool_link_settings',
                 'struct fib_rule_uid_range',
                 'struct statx',

src/basic/missing.h

@@ -1183,9 +1183,7 @@ struct input_mask {
 #define KEY_ALS_TOGGLE 0x230
 #endif
 
-#if ! HAVE_KEY_SERIAL_T
 typedef int32_t key_serial_t;
-#endif
 
 #ifndef KEYCTL_JOIN_SESSION_KEYRING
 #define KEYCTL_JOIN_SESSION_KEYRING 1