Fix some compilation warnings [neogb/msolve]

[vneiger]

This adds -Wall -Wextra -Wno-sign-compare -Wno-unused-parameter to the Makefile of the neogb and msolve components, and makes small fixes in the code to solve all the warnings that appeared.

None of the warnings revealed an actual issue, just one remains (at least on gcc with avx2):

In file included from msolve.c:25,
                 from libmsolve.c:35:
lifting-gb.c: In function 'verif_lifted_basis':
lifting-gb.c:1101:36: warning: the comparison will always evaluate as 'true' for the pointer operand in 'modgbs->modpolys + (sizetype)((long unsigned int)k * 48)' must not be NULL [-Waddress]
 1101 |             if(modgbs->modpolys[k] != NULL){

@mohabsafey could you please have a look to make sure != NULL is what you meant?

[mohabsafey]

I will have a look asap