Inadvertent dependency on libc `__stat_time64`

[AndrewFasano]

After #11, building libnvram for arm with newer compilers (i.e., arm-linux-musleabi-gcc (GCC) 11.2.1 20211120) adds a runtime dependency on the libc-provided __stat_time64 symbol:

nm  -D libnvram/libnvram.so.armel  | grep 'U '
...
U __stat_time64

This will break the library if it's used in older firmware where this symbol isn't provided by the firmware's libc; in this case an error will be raised when the library is loaded:

can't resolve symbol '__stat_time64'

[ddcc]

You can probably just pass a compile flag to have the compiler not do that, some variant of -fno-builtin-stat, -fno-builtin, or -ffreestanding. Or maybe -nostdlib -lc, I don't remember all the default libraries on Linux platforms.