__packed__ attribute ignored

[Helge Kruse]

While compiling an open source project (https://sigrok.org/) I
experience invalida code generated by MXE. It looks like the

__attribute__((__packed__))

is ignored for a structure. Here is the complete code to reproduce the
behavior:

#include <stdio.h>
#include <stddef.h>
#include <stdint.h>

typedef struct sample_config {
    uint32_t sample_depth;
    uint32_t psa;
    uint16_t u1;
    uint32_t u2;
    uint16_t clock_divisor;
} __attribute__((__packed__)) sample_config_t;

int main(int argc, char **argv)
{
    sample_config_t *pcfg = 0;
    printf("offset psa %lu\n", offsetof(sample_config_t,psa));
    printf("offset u1 %lu\n", offsetof(sample_config_t,u1));
    printf("offset u2 %lu\n", offsetof(sample_config_t,u2));
    printf("offset clock_divisor %lu\n",
offsetof(sample_config_t,clock_divisor));
}

The offset should be 4, 8, 10, 14, what can be verified with a normal
GCC build. The MX compiler for i686 and x86_64 uses offsets of 4, 8, 12,
16. i.e. it doesn't pack the structure.

$ $HOME/mxe-git/usr/bin/x86_64-w64-mingw32.static.posix-gcc --version
x86_64-w64-mingw32.static.posix-gcc (GCC) 5.5.0

How should that be fixed?

Best regards,
Helge