LibCore: Add mkfifo() syscall wrapper

Userland/Libraries/LibCore/System.cpp

@@ -945,4 +945,9 @@ ErrorOr<void> mknod(StringView pathname, mode_t mode, dev_t dev)
 #endif
 }
 
+ErrorOr<void> mkfifo(StringView pathname, mode_t mode)
+{
+    return mknod(pathname, mode | S_IFIFO, 0);
+}
+
 }

Userland/Libraries/LibCore/System.h

@@ -136,5 +136,6 @@ ErrorOr<void> getpeername(int sockfd, struct sockaddr*, socklen_t*);
 ErrorOr<void> socketpair(int domain, int type, int protocol, int sv[2]);
 ErrorOr<Vector<gid_t>> getgroups();
 ErrorOr<void> mknod(StringView pathname, mode_t mode, dev_t dev);
+ErrorOr<void> mkfifo(StringView pathname, mode_t mode);
 
 }