[Bug]: Some Lua binding symbol names are mangled in C++ compilation

[Suyooo]

What happened?

Since commit e4bdabc (Compile tolua++ output as C++), conky cannot find the luaopen_cairo symbol needed to initialize cairo, because the C++ compilation mangles the symbol name. Manually editing the tolua++ output to replace TOLUA_API with extern "C" fixes the problem, so it might be something that has to be changed in tolua++ more than conky itself.

Version

Git main branch (56a81ef)

Which OS/distro are you seeing the problem on?

Debian testing

Conky config

Minimal reproduction:

conky.config =
{
	own_window = true,
	lua_load = "test.lua",
	lua_draw_hook_post = "main",
}
conky.text = [[ ]];

test.lua

require 'cairo'

function conky_main()
	print("hello world")
end

Relevant log output

conky: desktop window (1e3) is root window
conky: window type - desktop
conky: drawing to created window (0x4e00002)
conky: drawing to double buffer
conky: llua_load: error loading module 'cairo' from file '/usr/local/lib/conky/libcairo.so':
	/usr/local/lib/conky/libcairo.so: undefined symbol: luaopen_cairo
conky: llua_do_call: function conky_main execution failed: attempt to call a nil value

Mangled symbols in libcairo.so:

$ nm -gD /usr/local/lib/conky/libcairo.so | grep _Z
0000000000012f40 T _Z13luaopen_cairoP9lua_State
0000000000010370 T _Z16tolua_cairo_openP9lua_State
00000000000102a0 T _Z21create_cairo_matrix_tv
0000000000010340 T _Z22destroy_cairo_matrix_tP13_cairo_matrix
0000000000010260 T _Z27create_cairo_font_extents_tv
0000000000010220 T _Z27create_cairo_text_extents_tv
0000000000010310 T _Z28destroy_cairo_font_extents_tP20cairo_font_extents_t
00000000000102e0 T _Z28destroy_cairo_text_extents_tP20cairo_text_extents_t
                 U _ZdaPv@GLIBCXX_3.4
                 U _Znam@GLIBCXX_3.4
                 U _Znwm@GLIBCXX_3.4

[brndnmtthws]

Of course, this seems obvious in hindsight.

I think #1750 should resolve it.