Add support for fflush and close syscalls

arch/x86_64.c

@@ -64,4 +64,28 @@ int32_t openat(int32_t fd, const char* filename, uint32_t flags, uint32_t mode)
   return file;
 }
 
+#define SYS_CLOSE 3
+int close(unsigned int fd) {
+  int rtn;
+  asm volatile(
+    "syscall"
+    : "=a"(rtn)
+    : "a"(SYS_CLOSE), "D"(fd)
+    : "rcx", "r11"
+  );
+  return rtn;
+}
+
+#define SYS_FSYNC 74
+int fsync(unsigned int fd) {
+  int rtn;
+  asm volatile(
+    "syscall"
+    : "=a"(rtn)
+    : "a"(SYS_FSYNC), "D"(fd)
+    : "rcx", "r11"
+  );
+  return rtn;
+}
+
 #endif /* ifdef __x86_64__ */