docs: Fix LUA_LIBDIR handling in example Makefile

See: #1257

On most platforms LUA_LIBDIR is empty, so you get:

Warning: unmatched variable LUA_LIBDIR

And the resulting empty -L flag in the example can cause issues like:

ld: warning: search path '-lpthread' not found

It's also not sufficient to pass the -L flag, you also have to provide the actual library to link.

I've updated the example to only set LUA_LIBDIR for windows where it is used by default. However, as noted in it is possible to do:

luarocks config link_lua_explicitly true

It would be better to respect this setting rather than hard-coding windows only, but I'm not sure the best way to check that config in the rockspec, I wonder if anyone else has any suggestions?

[docs] Use implicit rules in example makefile

See:
https://www.gnu.org/software/make/manual/html_node/Catalogue-of-Rules.html#index-C_002c-rule-to-compile
https://www.gnu.org/software/make/manual/html_node/Catalogue-of-Rules.html#index-linking_002c-predefined-rule-for
https://www.gnu.org/software/make/manual/html_node/Implicit-Variables.html#index-CPPFLAGS
https://www.gnu.org/software/make/manual/html_node/Implicit-Variables.html#index-LDFLAGS

[docs] Fix LUA_LIBDIR handling in makefile example

The example setup given here gives this warning on most systems:
```
Warning: unmatched variable LUA_LIBDIR
```

Also, you get an empty `-L` flag, which one some compilers will eat the
following flag, causing issues, e.g.
```
ld: warning: search path '-lpthread' not found
```

This is because most environments do not require explicit linking of
LUALIB, so it LUA_LIBDIR not set.

This patch fixes the sample by only setting `LUA_LIBDIR` when it
is actually needed, i.e. on windows.

[docs] Fix example makefile for windows

On windows, LUALIB is set to e.g. `lua51.dll`, which is the full name
and does not work with `-llua51.dll`. Passing the full path here allows
it to be linked properly.

Another option is `-l:$(LUALIB)` to specify the full file name, but some
linkers do not support that syntax.

[docs] Fix broken formatting due to unescaped $

[docs] Highlight makefile syntax

[docs] Use consistent whitespace

Fixes markdown warnings about hard tabs

0 files changed, 0 insertions, 0 deletions