Two attributes are currently defined for x86 configurations:
packed is used on a structure, or if bit-fields are used
it may be that the Microsoft ABI packs them differently
than GCC normally packs them. Particularly when moving packed
data between functions compiled with GCC and the native Microsoft compiler
(either via function call or as data in a file), it may be necessary to access
gcc_struct attributes correspond
to the -mms-bitfields and -mno-ms-bitfields
command-line options, respectively;
see x86 Options, for details of how structure layout is affected.
See x86 Variable Attributes, for information about the corresponding
attributes on variables.