Update comments in nolibc' signal.h

Rephrase the comments to catch up with the evolutions of signal.h

Co-authored-by: Fabrice Buoro <fabrice@tarides.com>

nolibc/include/signal.h

@@ -1,6 +1,13 @@
 #ifndef _SIGNAL_H
 #define _SIGNAL_H
 
+/*
+ * The following definitions are required not only to build the OCaml runtime
+ * but also the freestanding version of GMP used by Mirage.
+ * Note though that Solo5 does not implement signals, so we should not trigger a
+ * situation where these values are really used.
+ */
+
 typedef int jmp_buf;
 int setjmp(jmp_buf);
 void (*signal(int sig, void (*func)(int)))(int);
@@ -9,15 +16,7 @@ void (*signal(int sig, void (*func)(int)))(int);
 #define SIG_ERR 0
 #define SIG_BLOCK 0
 #define SIG_SETMASK 0
-/*
- * The following definitions are not required by the OCaml runtime, but are
- * needed to build the freestanding version of GMP used by Mirage.
- * For OCaml 5.0.0, it's not totally true. SIG_{BLOCK,SETMASK,IGN,DFL) are
- * needed by the OCaml runtime.
- *
- * NOTE: Solo5 does not implement signals, but we should not trigger
- * a situation where these values are really used.
- */
+
 #define SIGFPE 1
 int raise(int);