Fix for warnings and errors from CLANG compiling

Instructions on how to run (credits to @schmidtr ):

1. Install clang (version 10)
2. apply the patch
3. do the following

cd openairinterface5g
mkdir build && cd build
export CC=/usr/bin/clang
export CXX=/usr/bin/clang++
cmake .. -GNinja
ninja nr-softmodem

patch