Linux: use 'SYS_wait4' instead of 'SYS_waitpid'

'SYS_waitpid' does not exist on x86_64 Linux, but 'SYS_wait4' does.

Fixes #615.

base-linux/src/core/include/core_linux_syscalls.h

@@ -112,7 +112,7 @@ inline int lx_setgid(unsigned int gid)
  */
 inline int lx_pollpid()
 {
-	return lx_syscall(SYS_waitpid, -1 /* any PID */, (int *)0, 1 /* WNOHANG */);
+	return lx_syscall(SYS_wait4, -1 /* any PID */, (int *)0, 1 /* WNOHANG */, 0);
 }
 
 

base-linux/src/core/include/platform_thread.h

@@ -27,7 +27,7 @@ namespace Genode {
 	/*
 	 * We hold all Platform_thread objects in a list in order to be able to
 	 * reflect SIGCHLD as exception signals. When a SIGCHILD occurs, we
-	 * determine the PID of the terminated child process via 'waitpid'. We use
+	 * determine the PID of the terminated child process via 'wait4'. We use
 	 * the list to find the 'Platform_thread' matching the TID, wherei, in
 	 * turn, we find the exception handler's 'Signal_context_capability'.
 	 */

base-linux/src/core/platform.cc

@@ -96,7 +96,7 @@ void Platform::wait_for_exit()
 		/*
 		 * Reflect SIGCHLD as exception signal to the signal context of the CPU
 		 * session of the process. Because multiple children could have been
-		 * terminated, we iterate until 'pollpid' (wrapper around 'waitpid')
+		 * terminated, we iterate until 'pollpid' (wrapper around 'wait4')
 		 * returns -1.
 		 */
 		for (;;) {