common: stat64 is non-standard, hide on a random Unix

src/common/file_util.cpp:79:19: error: variable has incomplete type 'struct stat64'
    struct stat64 file_info;
                  ^
src/common/file_util.cpp:79:12: note: forward declaration of 'stat64'
    struct stat64 file_info;
           ^
src/common/file_util.cpp:99:19: error: variable has incomplete type 'struct stat64'
    struct stat64 file_info;
                  ^
src/common/file_util.cpp:99:12: note: forward declaration of 'stat64'
    struct stat64 file_info;
           ^
src/common/file_util.cpp:342:19: error: variable has incomplete type 'struct stat64'
    struct stat64 buf;
                  ^
src/common/file_util.cpp:342:12: note: forward declaration of 'stat64'
    struct stat64 buf;
           ^
src/common/file_util.cpp:359:19: error: variable has incomplete type 'struct stat64'
    struct stat64 buf;
                  ^
src/common/file_util.cpp:359:12: note: forward declaration of 'stat64'
    struct stat64 buf;
           ^
4 errors generated.