Rename libmsl to libsystem

libsystem/amd64/syscall.c

@@ -0,0 +1,17 @@
+#include <amd64/syscall.h>
+#include <stddef.h>
+#include <stdint.h>
+
+uintptr_t amd64_syscall (int syscall_num, uintptr_t a1, uintptr_t a2, uintptr_t a3, uintptr_t a4,
+                         uintptr_t a5, uintptr_t a6) {
+  uint64_t result;
+  __asm__ volatile ("movq %[a4], %%r10\n"
+                    "movq %[a5], %%r8\n"
+                    "movq %[a6], %%r9\n"
+                    "syscall\n"
+                    : "=a"(result)
+                    : "a"(syscall_num), "D"(a1), "S"(a2),
+                      "d"(a3), [a4] "r"(a4), [a5] "r"(a5), [a6] "r"(a6)
+                    : "r10", "r8", "r9", "r11", "rcx", "cc", "memory");
+  return result;
+}