package/luvi: add upstream patch to fix runtime issue with CMake 3.12+

package/luvi: add upstream patch to fix runtime issue with CMake 3.12+

luvi fails to run when it was build with CMake 3.12+:

```
[string "return require('init')(...)"]:1: module 'init' not found:
	no field package.preload['init']
	no file './init.lua'
	no file '/usr/share/luajit-2.0.5/init.lua'
	no file '/usr/local/share/lua/5.1/init.lua'
	no file '/usr/local/share/lua/5.1/init/init.lua'
	no file '/usr/share/lua/5.1/init.lua'
	no file '/usr/share/lua/5.1/init/init.lua'
	no file './init.so'
	no file '/usr/local/lib/lua/5.1/init.so'
	no file '/usr/lib/lua/5.1/init.so'
	no file '/usr/local/lib/lua/5.1/loadall.so'
```

Looking at link.txt for the luvi executable shows that `-rdynamic` is
not set anymore in CMake 3.12. This has the effect, that symbols are
missing in the `.dynsym` section in the binary.

The patch, sets `ENABLE_EXPORTS` to true in CMakeLists.txt to force setting
`-rdynamic` explicitly.

Upstream status: b8781653dcb8815a3019a77baf4f3b7f7a255ebe

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>