fix previous; check for C99 compound literals

The previous commit was incorrect (or at least insufficient), the
ML-KEM code is actually using compound literals, so test for them.

configure.ac

@@ -353,16 +353,17 @@ AC_COMPILE_IFELSE(
  [ AC_MSG_RESULT([no]) ]
 )
 
-AC_MSG_CHECKING([if compiler supports named struct initialisers])
+AC_MSG_CHECKING([if compiler supports compound literals])
 AC_COMPILE_IFELSE(
  [AC_LANG_PROGRAM([[#include <stdlib.h>]],
- [[ struct foo { int bar; int baz; };
- struct foo blerg = {.bar = 1, .baz = 2};
- exit((blerg.bar == 1 && blerg.baz == 2) ? 0 : 1);
+ [[ struct foo { int bar; int baz; };
+ void *fooc = &(struct foo){.bar = 1, .baz = 2};
+ struct foo *foo2 = (struct foo *)fooc;
+ return (foo2->bar == 1 && foo2->baz == 2) ? 0 : 1;
  ]])],
  [ AC_MSG_RESULT([yes])
- AC_DEFINE(NAMED_STRUCT_INITIALISERS, [1],
- [compiler supports named struct initializers]) ],
+ AC_DEFINE(COMPOUND_LITERALS, [1],
+ [compiler supports compound literals]) ],
  [ AC_MSG_RESULT([no]) ]
 )
 

defines.h

@@ -942,8 +942,8 @@ struct winsize {
 #if defined(VARIABLE_LENGTH_ARRAYS) && defined(VARIABLE_DECLARATION_AFTER_CODE)
 # define USE_SNTRUP761X25519 1
 #endif
-/* The ML-KEM768 imlementation similarly uses named struct initialisers */
-#ifdef NAMED_STRUCT_INITIALISERS
+/* The ML-KEM768 imlementation similarly uses C99 compound literals */
+#ifdef COMPOUND_LITERALS
 # define USE_MLKEM768X25519 1
 #endif
 #endif /* _DEFINES_H */