utilise _FILE_OFFSET_BITS=64

[nekopsykose]

Describe the bug

building btop with a recent commit of musl will fail, with:

/home/demon/src/aports/community/btop/src/btop-1.2.13/src/linux/btop_collect.cpp:1082:23: error: variable has incomplete type 'struct statvfs64'
                                        struct statvfs64 vfs;
                                                         ^
/home/demon/src/aports/community/btop/src/btop-1.2.13/src/linux/btop_collect.cpp:1082:13: note: forward declaration of 'statvfs64'
                                        struct statvfs64 vfs;
                                               ^
/home/demon/src/aports/community/btop/src/btop-1.2.13/src/linux/btop_collect.cpp:1083:46: error: invalid operands to binary expression ('statvfs64' and 'int')
                                        if (statvfs64(mountpoint.c_str(), &vfs) < 0) {
                                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~

this is because of bminor/musl@25e6fee , but the reason is mostly that the 64 interfaces are legacy; they are from a period where they were created for transitional reasons.

in modern programming, it suffices to pass -D_FILE_OFFSET_BITS=64, and to utilise the non-64 name, i.e. statvfs, and the types are 64-bit on linux. see e.g. the glibc docs for it: https://www.gnu.org/software/libc/manual/html_node/Feature-Test-Macros.html . in musl, the non-64 names were always 64-bit; the 64 wrappers were added as a compatibility shim that are now not exposed (and will eventually be removed, left in ABI compat only).

To Reproduce

build against musl since bminor/musl@25e6fee without passing -D_LARGEFILE64_SOURCE