fix(rockspec): Check for Lua 5.1 header files.

Previously, rockspec.lua checked if Lua 5.1 was installed to determine
if LuaRocks could build packages for Lua 5.1. This was not sufficient
since the Lua version does not matter as long as the development headers
for Lua 5.1 are available. So Lua 5.1 could be installed and the
LuaRocks packages could still fail to install.

Note: this also checks if a suitable version of Lua is installed since
      the command will fail if Lua is not installed at all.

lua/lazy/pkg/rockspec.lua

@@ -4,6 +4,7 @@ local Community = require("lazy.community")
 local Config = require("lazy.core.config")
 local Health = require("lazy.health")
 local Util = require("lazy.util")
+local Process = require("lazy.manage.process")
 
 ---@class RockSpec
 ---@field rockspec_format string
@@ -63,6 +64,21 @@ function M.hererocks.building()
   return vim.tbl_get(Config.plugins.hererocks or {}, "_", "build")
 end
 
+---@param opts? LazyHealth
+---@param luarocks_cmd string
+---@return boolean
+function M.check_lua51_headers(opts, luarocks_cmd)
+  local cmd = { luarocks_cmd, "--lua-version=5.1", "config", "variables.LUA_INCDIR" }
+  local _, exit_code = Process.exec(cmd)
+  
+  if exit_code ~= 0 then
+    opts.error("Lua 5.1 headers not found. Install the Lua 5.1 development package for your system.")
+    return false
+  end
+  
+  return true
+end
+
 ---@param opts? LazyHealth
 function M.check(opts)
   opts = vim.tbl_extend("force", {
@@ -78,23 +94,23 @@ function M.check(opts)
     else
       ok = Health.have(M.python, opts)
       ok = Health.have(M.hererocks.bin("luarocks")) and ok
-      Health.have(
+      if ok then
-        M.hererocks.bin("lua"),
+        local luarocks_cmd = M.hererocks.bin("luarocks")
-        vim.tbl_extend("force", opts, {
+        if Util.is_win then
-          version = "-v",
+          luarocks_cmd = luarocks_cmd .. ".bat"
-          version_pattern = "5.1",
+        end
-        })
+        ok = M.check_lua51_headers(opts, luarocks_cmd)
-      )
+      end
     end
   else
     ok = Health.have("luarocks", opts)
-    Health.have(
+    if ok then
-      { "lua5.1", "lua", "lua-5.1" },
+      local luarocks_cmd = "luarocks"
-      vim.tbl_extend("force", opts, {
+      if Util.is_win then
-        version = "-v",
+        luarocks_cmd = luarocks_cmd .. ".bat"
-        version_pattern = "5.1",
+      end
-      })
+      ok = M.check_lua51_headers(opts, luarocks_cmd)
-    )
+    end
   end
   return ok
 end