Kernel/LibC: Add initial pseudo terminal support

This patch implements posix_openpt() and ptsname()

grantpt() and unlockpt() are left in LibC as stubs, as posix_openpt
currently does all of the needed work.

kernel/CMakeLists.txt

@@ -86,6 +86,7 @@ set(KERNEL_SOURCES
 	kernel/Storage/StorageDevice.cpp
 	kernel/Syscall.cpp
 	kernel/Terminal/FramebufferTerminal.cpp
+	kernel/Terminal/PseudoTerminal.cpp
 	kernel/Terminal/Serial.cpp
 	kernel/Terminal/TTY.cpp
 	kernel/Terminal/VirtualTTY.cpp