Kernel, libc: Add ECHILD

kernel/include/std/errno.h

@@ -7,6 +7,7 @@
 #define E2BIG 7
 #define ENOEXEC 8
 #define EBADF 9
+#define ECHILD 10
 #define EAGAIN 11
 #define ENOMEM 12
 #define EACCES 13

libs/libc/include/errno.h

@@ -12,6 +12,7 @@ extern int errno;
 #define E2BIG 7       // Argument list too long
 #define ENOEXEC 8     // Exec format error
 #define EBADF 9       // Bad file descriptor
+#define ECHILD 10     // No child processes
 #define EAGAIN 11     // Resource temporarily unavailable
 #define ENOMEM 12     // Cannot allocate memory
 #define EACCES 13     // Permission denied

libs/libc/src/string.cpp

@@ -265,6 +265,7 @@ extern "C"
         case E2BIG: return "Argument list too long";
         case ENOEXEC: return "Exec format error";
         case EBADF: return "Bad file descriptor";
+        case ECHILD: return "No child processes";
         case EAGAIN: return "Resource temporarily unavailable";
         case ENOMEM: return "Cannot allocate memory";
         case EACCES: return "Permission denied";