Code doesn't compile on Ubuntu 21.04: ld returned 1 exit status

[Tc14Hd]

When I run the command ./configure && make, I get a long error message that ends with:

collect2: error: ld returned 1 exit status
make: *** [Makefile:31: cadet] Error 1

The full error message can be found here.
Am I doing something wrong or is this an actual problem? I am using GCC version 10.3.0 on Ubuntu 21.04.

[player1537]

I believe the cause of this compile error is that src/log.h needs to have extern added before each of the variable declarations.

Specifically, lines 39-42 of src/log.h should be changed from:

int debug_verbosity;
bool log_qdimacs_compliant;
bool log_colors;
bool log_silent;

to:

extern int debug_verbosity;
extern bool log_qdimacs_compliant;
extern bool log_colors;
extern bool log_silent;

This was tested and it seems to be working now.