fix: create liblualib.a symlink for Lua 5.1+ installs

[tyrro]

Problem

Since Lua 5.1, liblualib was merged into liblua. Lua 5.1+ installs built from source only produce liblua.a, but older native extensions (e.g. the ruby-lua gem) still link against -llualib. This causes the build to fail:

ld: library 'lualib' not found

Solution

After copying the Lua files to the install path, create a liblualib.a → liblua.a symlink when:

• The version is Lua 5.1 or greater (not LuaJIT — LuaJIT uses different lib naming)
• liblua.a is present in the install's lib/ directory
• liblualib.a does not already exist (no-op if a future release ships it again)

if [ "${lua_type}" != "LuaJIT" ] && version_5_1x_or_greater "$version"; then
  if [ -f "${install_path}/lib/liblua.a" ] && [ ! -e "${install_path}/lib/liblualib.a" ]; then
    ln -sf "${install_path}/lib/liblua.a" "${install_path}/lib/liblualib.a"
  fi
fi

This matches what package managers like Homebrew do when installing Lua.

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[tyrro]

@Stratus3D the CI is failing

FAILED: lua was not properly installed reason: unable to clone plugin: fatal: Remote branch fix/liblualib-symlink-lua-5-1-plus not found in upstream origin

any suggestion to fix it?

[Stratus3D]

I'm closing this PR. See #39 (comment)