lib: onigmo: CMakeLists.txt: fix build without C++

onigmo is written in c, so only enforce a c compiler

upstream: fluent/onigmo#7

Signed-off-by: Thomas Devoogdt <thomas.devoogdt@barco.com>

Author: ThomasDevoogdt

lib/onigmo/CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.4)
-project(onigmo)
+project(onigmo C)
 
 # Onigmo Version
 set(ONIGMO_VERSION_MAJOR  6)