[CORE] Eliminate compile warnings

[zengdage]

As per ptitSeb's requirements, patches addressing compiler warnings may only be merged after the 0.4.4 release. This PR is solely for pre‑review at this stage.

1. vasprintf can return a negative value and buff may be NULL.

2. The events argument in epoll_pwait must not be NULL.

3. The size of val.f.q is 64 bits.

[zengdage]

@devarajabc This pr addresses compiler‑warnings.

[ptitSeb]

why 64? 344+1 is exactly the size the branding should be (3 sets of 4 32bits registers) + terminal 0

[zengdage]

The actual output of this statement can exceed 49 bytes, hence the warning shown below.

snprintf(branding, sizeof(branding), "Box64 v0.4.3 on %.\*s", 39, box64\_sysinfo.cpuname);

/usr/include/riscv64-linux-gnu/bits/stdio2.h:68:10: note: ‘__builtin___snprintf_chk’ output between 27 and 55 bytes into a destination of size 49
 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 |                                    __glibc_objsize (__s), __fmt,
      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 |                                    __va_arg_pack ());

[ptitSeb]

I have fixed the issue in a separate commit. It make no sense to build a brand bigger than needed.

[zengdage]

Sorry, your changes did not fully eliminate the warning.

1. At line 190, only 31 characters are available for cpuname;
2. At lines 193 and 195, only 21 characters can be printed for cpuname, since @%1.2f GHz consumes 10 characters.

This is not a fatal overflow. Because snprintf enforces the buffer‑size limit, real buffer overflow cannot happen. The warning only suggests potential truncation of output. There is no impact even without a fix.

/usr/include/riscv64-linux-gnu/bits/stdio2.h:68:10: note: ‘__builtin___snprintf_chk’ output between 17 and 49 bytes into a destination of size 48
   68 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   69 |                                    __glibc_objsize (__s), __fmt,
      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   70 |                                    __va_arg_pack ());

/usr/include/riscv64-linux-gnu/bits/stdio2.h:68:10: note: ‘__builtin___snprintf_chk’ output between 27 and 55 bytes into a destination of size 48
   68 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   69 |                                    __glibc_objsize (__s), __fmt,
      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   70 |                                    __va_arg_pack ());