gplugin/gplugin

Fix an issue where meson would fail if building without gtk3 support

2021-04-28, Gary Kramlich
b7c659d32d7a
Fix an issue where meson would fail if building without gtk3 support

Testing Done:
Ran `meson` (with no options) and verified that `ninja doc` built both `gplugin-doc` and `gplugin-gtk-doc`.

Ran `meson -Dgtk3=false` and verified that `ninja doc` just built `gplugin-doc`

Reviewed at https://reviews.imfreedom.org/r/629/
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`.