Может с разными стандартами компилируются файлы? "In Standard C, int, signed int, and unsigned int can be used as the base type for
integer bitfields. In standard C++, and in C when language extensions are enabled in the
compiler, any integer or enumeration type can be used as the base type. It is
implementation defined whether a plain integer type (char, short, int, etc) results in
a signed or unsigned bitfield."