Revert "examples/ucontext-cp.c: Do not use SIGSTKSZ"

This reverts commit af31ce2c.

The commit is buggy and causes ucontext-cp to crash. Just revert it
for now.

Fixes: https://github.com/axboe/liburing/issues/459


Signed-off-by: Jens Axboe <axboe@kernel.dk>

examples/ucontext-cp.c

@@ -3,7 +3,6 @@
  * gcc -Wall -O2 -D_GNU_SOURCE -o ucontext-cp ucontext-cp.c -luring
  */
 #define _POSIX_C_SOURCE 199309L
-#include <stddef.h>
 #include <stdio.h>
 #include <fcntl.h>
 #include <string.h>
@@ -23,7 +22,9 @@
 #define QD	64
 #define BS	1024
 
-size_t sigstksz = (8 * 1024 + sizeof (max_align_t) - 1) / sizeof (max_align_t);
+#ifndef SIGSTKSZ
+#define SIGSTKSZ 8192
+#endif
 
 typedef struct {
 	struct io_uring *ring;
@@ -114,13 +115,13 @@ static int setup_context(async_context *pctx, struct io_uring *ring)
 		perror("getcontext");
 		return -1;
 	}
-	pctx->stack_buf = malloc(sigstksz);
+	pctx->stack_buf = malloc(SIGSTKSZ);
 	if (!pctx->stack_buf) {
 		perror("malloc");
 		return -1;
 	}
 	pctx->ctx_fnew.uc_stack.ss_sp = pctx->stack_buf;
-	pctx->ctx_fnew.uc_stack.ss_size = sigstksz;
+	pctx->ctx_fnew.uc_stack.ss_size = SIGSTKSZ;
 	pctx->ctx_fnew.uc_link = &pctx->ctx_main;
 
 	return 0;