Receiving the following error during compilation of the port with CLANG. /etc/make.conf is setup as recommended by the WIKI.

1 warning generated.
CC      libavcodec/x86/lpc_mmx.o
CC      libavcodec/x86/mlpdsp.o
CC      libavcodec/x86/motion_est_mmx.o
CC      libavcodec/x86/mpegvideo_mmx.o
CC      libavcodec/x86/simple_idct_mmx.o
CC      libavcodec/x86/snowdsp_mmx.o
CC      libavcodec/x86/vc1dsp_mmx.o
libavcodec/x86/snowdsp_mmx.c:848:10: error: ambiguous instructions require an explicit suffix (could be 'addb', 'addw', 'addl', or 'addq')
snow_inner_add_yblock_mmx_end("32")
^
libavcodec/x86/snowdsp_mmx.c:813:48: note: instantiated from:
             "add %%"REG_c", (%%"REG_a")     \n\t"\
                                               ^
<inline asm>:139:2: note: instantiated into assembly here
        add $8*1, 56(%rsp)          
        ^
libavcodec/x86/snowdsp_mmx.c:831:10: error: ambiguous instructions require an explicit suffix (could be 'addb', 'addw', 'addl', or 'addq')
snow_inner_add_yblock_mmx_end("16")
^
libavcodec/x86/snowdsp_mmx.c:813:48: note: instantiated from:
             "add %%"REG_c", (%%"REG_a")     \n\t"\
                                               ^
<inline asm>:78:2: note: instantiated into assembly here
        add $8*1, 96(%rsp)          
        ^
2 errors generated.
gmake: *** [libavcodec/x86/snowdsp_mmx.o] Error 1
gmake: *** Waiting for unfinished jobs....
libavcodec/x86/dsputil_mmx.c:609:10: error: invalid operand for instruction
        "movzx (%3,%4), %2 \n"
         ^
<inline asm>:3:20: note: instantiated into assembly here
movzx (%rcx,%r11), %r10d 
                   ^
3 warnings and 1 error generated.
gmake: *** [libavcodec/x86/dsputil_mmx.o] Error 1
*** Error code 1

Stop in /usr/ports/multimedia/ffmpeg.
*** Error code 1

Stop in /usr/ports/multimedia/ffmpeg.

===>>> make failed for multimedia/ffmpeg
===>>> Aborting update

===>>> Update for multimedia/ffmpeg failed
===>>> Aborting update