Kernel: Implement SYS_SYNC and add sync executable to userspace

You can (and have to) manually sync disk after writes to it.

userspace/CMakeLists.txt

@@ -12,6 +12,7 @@ set(USERSPACE_PROJECTS
 	Shell
 	snake
 	stat
+	sync
 	tee
 	test
 	touch

userspace/sync/CMakeLists.txt

@@ -0,0 +1,17 @@
+cmake_minimum_required(VERSION 3.26)
+
+project(sync CXX)
+
+set(SOURCES
+	main.cpp
+)
+
+add_executable(sync ${SOURCES})
+target_compile_options(sync PUBLIC -O2 -g)
+target_link_libraries(sync PUBLIC libc)
+
+add_custom_target(sync-install
+	COMMAND sudo cp ${CMAKE_CURRENT_BINARY_DIR}/sync ${BANAN_BIN}/
+	DEPENDS sync
+	USES_TERMINAL
+)

userspace/sync/main.cpp

@@ -0,0 +1,6 @@
+#include <unistd.h>
+
+int main()
+{
+	sync();
+}