gplugin/gplugin

Print out the error if testing for lgi failed.

2021-03-11, Elliott Sales de Andrade
2dedd64d03b9
Print out the error if testing for lgi failed.

This will be swallowed by Meson, so is not noisy, but will appear in the logs
for easier debugging.

Testing Done:
Compiled in mingw, which has some path issues with Lua, which can now be found in the error in the logs.

Reviewed at https://reviews.imfreedom.org/r/569/
There are a few notes about building on OSX.
First off, building has *ONLY* been tested against homebrew. If you want to
support fink or macports, please let me know and I will merge your pull
request.
Currently there is no known way to build the Perl loader on MacOS. So you
**MUST** run meson with `-Dperl5=false`.
## Lua
For the Lua loader to work, you need to install `lgi` from luarocks either
systemwide for lua 5.1 as `lgi` does not currently work with lua 5.4 which is
the default in homebrew.
To make this work, you'll need to install both `lua@5.1` and `luarocks` via
`brew install lua@5.1 luarocks`. Once those are installed, you'll need to
create `/usr/local/etc/luarocks/config-5.1.lua` with the following contents.
```
-- LuaRocks configuration
rocks_trees = {
{ name = "user", root = home .. "/.luarocks" };
{ name = "system", root = "/usr/local" };
}
lua_interpreter = "lua5.1";
variables = {
LUA_DIR = "/usr/local/opt/lua@5.1";
LUA_BINDIR = "/usr/local/opt/lua@5.1/bin";
}
```
Once that is done, you can then finally install `lgi` with the following
command.
```
luarocks --lua-version=5.1 install lgi
```
## Python3
If you're using homebrew, you need to install `pygobject3`.