linux-user: fix fork()

Since commit 5ea2fc8 ("linux-user: Sanity check clone flags"),
trying to run fork() fails with old distro on some architectures.

This is the case with HP-PA and Debian 5 (Lenny).

It fails on:

         if ((flags & CSIGNAL) != TARGET_SIGCHLD) {
             return -TARGET_EINVAL;
         }

because flags is 17, whereas on HP-PA, SIGCHLD is 18.
17 is the SIGCHLD value of my host (x86_64).

It appears that for TARGET_NR_fork and TARGET_NR_vfork, QEMU calls
do_fork() with SIGCHLD instead of TARGET_SIGCHLD.

Signed-off-by: Laurent Vivier <[email protected]>
Reviewed-by: Peter Maydell <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-Id: <[email protected]>

linux-user/syscall.c

@@ -7680,7 +7680,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
         break;
 #ifdef TARGET_NR_fork
     case TARGET_NR_fork:
-        ret = get_errno(do_fork(cpu_env, SIGCHLD, 0, 0, 0, 0));
+        ret = get_errno(do_fork(cpu_env, TARGET_SIGCHLD, 0, 0, 0, 0));
         break;
 #endif
 #ifdef TARGET_NR_waitpid
@@ -10490,7 +10490,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
 #endif
 #ifdef TARGET_NR_vfork
     case TARGET_NR_vfork:
-        ret = get_errno(do_fork(cpu_env, CLONE_VFORK | CLONE_VM | SIGCHLD,
+        ret = get_errno(do_fork(cpu_env,
+                        CLONE_VFORK | CLONE_VM | TARGET_SIGCHLD,
                         0, 0, 0, 0));
         break;
 #endif