OK, -fno-common seems to have fixed the alignment, from the map file,

`Module: K:\work\ffmpeg\src\ffmpeg.obj\libavcodec\fft_fixed.o(src\libavcodec\fft_fixed.c)`

0001:001fbc83 _ff_init_ff_cos_tabs_fixed

0001:001fc050 _ff_cos_tabs_fixed

0001:001fbd3c _ff_fft_init_fixed

0001:001fbf90 _ff_fft_end_fixed

0002:001cc900 _ff_cos_131072_fixed

0002:0020c8e0 _ff_cos_16_fixed

0002:0020c8c0 _ff_cos_32_fixed

0002:0020c880 _ff_cos_64_fixed

0002:0020c800 _ff_cos_128_fixed

0002:0020c700 _ff_cos_256_fixed

0002:0020c500 _ff_cos_512_fixed

0002:0020c100 _ff_cos_1024_fixed

0002:0020b900 _ff_cos_2048_fixed

0002:0020a900 _ff_cos_4096_fixed

0002:00208900 _ff_cos_8192_fixed

0002:00204900 _ff_cos_16384_fixed

0002:001fc900 _ff_cos_32768_fixed

0002:001ec900 _ff_cos_65536_fixed

...

`Module: K:\work\ffmpeg\src\ffmpeg.obj\libavcodec\fft_float.o(src\libavcodec\fft_float.c)`

0001:002114e0 _ff_init_ff_cos_tabs

0001:00211870 _ff_cos_tabs

0001:00211561 _ff_fft_init

0001:002117bc _ff_fft_end

0002:0020c900 _ff_cos_131072

0002:0028c8c0 _ff_cos_16

0002:0028c880 _ff_cos_32

0002:0028c800 _ff_cos_64

...

Edit, BTW, GCC outputs aout