Add stage 06: Lua bootstrap

The goal of stage 06 is to try parse zig synax in lua. I pulled in
lpeglable 1.2.0 and parser-gen off github to get started. All of this
needs to be cleaned up rather soon.

Lua boostraps using tcc and musl from the previous stage. Since musl
0.6.0 doesn't support dynamic linking this build of lua doesn't support
shared libraries. I couldn't easily patch musl with dlopen and friends
so instead I link statically and call deps with c api.

06/lua-5.4.6/src/lzio.c

@@ -0,0 +1,68 @@
+/*
+** $Id: lzio.c $
+** Buffered streams
+** See Copyright Notice in lua.h
+*/
+
+#define lzio_c
+#define LUA_CORE
+
+#include "lprefix.h"
+
+
+#include <string.h>
+
+#include "lua.h"
+
+#include "llimits.h"
+#include "lmem.h"
+#include "lstate.h"
+#include "lzio.h"
+
+
+int luaZ_fill (ZIO *z) {
+  size_t size;
+  lua_State *L = z->L;
+  const char *buff;
+  lua_unlock(L);
+  buff = z->reader(L, z->data, &size);
+  lua_lock(L);
+  if (buff == NULL || size == 0)
+    return EOZ;
+  z->n = size - 1;  /* discount char being returned */
+  z->p = buff;
+  return cast_uchar(*(z->p++));
+}
+
+
+void luaZ_init (lua_State *L, ZIO *z, lua_Reader reader, void *data) {
+  z->L = L;
+  z->reader = reader;
+  z->data = data;
+  z->n = 0;
+  z->p = NULL;
+}
+
+
+/* --------------------------------------------------------------- read --- */
+size_t luaZ_read (ZIO *z, void *b, size_t n) {
+  while (n) {
+    size_t m;
+    if (z->n == 0) {  /* no bytes in buffer? */
+      if (luaZ_fill(z) == EOZ)  /* try to read more */
+        return n;  /* no more input; return number of missing bytes */
+      else {
+        z->n++;  /* luaZ_fill consumed first byte; put it back */
+        z->p--;
+      }
+    }
+    m = (n <= z->n) ? n : z->n;  /* min. between n and z->n */
+    memcpy(b, z->p, m);
+    z->n -= m;
+    z->p += m;
+    b = (char *)b + m;
+    n -= m;
+  }
+  return 0;
+}
+