Why clone coin that compiled in ubuntu 16.04 cannot compile in ubuntu 18.04?

[linz]

I compiled and generate first block an cloned coin (POW/POS) on ubuntu 16.04.
For desktop wallet development .need to install mxe packages ( cross compile ).
it cannot be install by ubuntu 16.04 (gcc version low)
It need gcc version 9 .So I upgrade to ubuntu 18.04 and install gcc ver 9.2.0
install syccessfully cross compile packages but cannot compile cloned coin.
It show error 4 times
1st is error in obj directory
solve by sudo mkdir obj
2nd error is zerocoin directory
solve by #src sudo mkdir obj/zerocoin
3rd error is leveldb
solve by
cd leveldb
chmod 755 *
cd ..
and compile again

4th error is
  ^{/usr/bin/ld: final link failed: Nonrepresentable section on output collect2: error: ld returned 1 exit status makefile.unix:189: recipe for target 'mconnectd' failed make: *** [mconnectd] Error 1} 

I checked src file .it missing mconnectd file that generated by compiling.

Why this happen in ubuntu 18.04.

How can solve it?

Can install cross compile window package by low gcc version?

Can I know compiling guide for POWPOS in ubuntu 18.04.

[NotATether]

If you are looking for support to compile an altcoin, you'll need to get in touch with the altcoin developers about this issue so they can help you. It's unlikely there's anyone here who is familiar with the coin you are trying to compile.

That ld error looks like a problem with the makefile process of the altcoin rather than something on your operating system.

[HCP]

Does this altcoin not have any compilation instructions on their github (or similar) repository?

Usually, any minimum system requirements and/or specific software version requirements are mentioned there. If they aren't, contact the altcoin dev's and ask them.