Remove a lot of "unused parameter" warnings (#3075)

They might shadow some of the real issues, so better to keep the number
of warnings as low as possible.

core/shared/platform/common/posix/posix_blocking_op.c

@@ -15,6 +15,7 @@ static void
 blocking_op_sighandler(int signo)
 {
     /* nothing */
+    (void)signo;
 }
 
 void

core/shared/platform/common/posix/posix_clock.c

@@ -73,6 +73,8 @@ os_clock_time_get(__wasi_clockid_t clock_id, __wasi_timestamp_t precision,
     clockid_t nclock_id;
     __wasi_errno_t error = wasi_clockid_to_clockid(clock_id, &nclock_id);
 
+    (void)precision;
+
     if (error != __WASI_ESUCCESS)
         return error;
 

core/shared/platform/common/posix/posix_memmap.c

@@ -266,5 +266,8 @@ os_icache_flush(void *start, size_t len)
 {
 #if defined(__APPLE__) || defined(__MACH__)
     sys_icache_invalidate(start, len);
+#else
+    (void)start;
+    (void)len;
 #endif
 }