rockspec: propagate CMake options

Sometimes one needs to build a luzer module using rockspec with
a non-system Lua library and headers, for which the CMake options
LUA_LIBRARIES and LUA_INCLUDE_DIR are used. The patch adds
variables for the rockspec to set these options via environment
variables: CMAKE_LUA_LIBRARIES, CMAKE_LUA_INCLUDE_DIR,
ENABLE_LUAJIT and LUAJIT_FRIENDLY_MODE.

luarocks install --lua-version 5.1 --verbose --tree=lua_modules \
  luzer-scm-1.rockspec ENABLE_LUAJIT=ON LUAJIT_FRIENDLY_MODE=ON

Needed for google/oss-fuzz#14610

Author: ligurio

CMakeLists.txt

@@ -16,6 +16,16 @@ endif()
 set(CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
 include(SetClangRTLib)
 
+# It is not possible to pass LUA_LIBRARIES and LUA_INCLUDE_DIR
+# directly because it breaks `find_package(Lua)`, so it is done
+# using intermediate variables.
+if(NOT "${CMAKE_LUA_LIBRARIES}" STREQUAL "")
+  set(LUA_LIBRARIES "${CMAKE_LUA_LIBRARIES}")
+endif()
+if(NOT "${CMAKE_LUA_INCLUDE_DIR}" STREQUAL "")
+  set(LUA_INCLUDE_DIR "${CMAKE_LUA_INCLUDE_DIR}")
+endif()
+
 if(LUA_INCLUDE_DIR AND LUA_LIBRARIES)
   # When a path to a Lua library is passed outside, we should
   # mimic a real CMake library to don't break code that depends on

luzer-scm-1.rockspec

@@ -26,6 +26,10 @@ build = {
     -- https://github.com/luarocks/luarocks/blob/7ed653f010671b3a7245be9adcc70068c049ef68/docs/config_file_format.md#config-file-format
     -- luacheck: pop
     variables = {
+        ENABLE_LUAJIT = "$(ENABLE_LUAJIT)",
+        LUAJIT_FRIENDLY_MODE = "$(LUAJIT_FRIENDLY_MODE)",
+        CMAKE_LUA_INCLUDE_DIR = "$(LUA_INCLUDE_DIR)",
+        CMAKE_LUA_LIBRARIES = "$(LUA_LIBRARIES)",
         CMAKE_LUADIR = "$(LUADIR)",
         CMAKE_LIBDIR = "$(LIBDIR)",
         CMAKE_BUILD_TYPE = "RelWithDebInfo",