RPI3, error: invalid operand in inline asm: 'rev16 ${0:w}, ${1:w}'

[bob prohaska]

In a recent attempt to compile www/chromium on an RPI3 running r345516
compilation stopped with repeated reports of 

/usr/include/machine/endian.h:89:19: error: invalid operand in inline asm: 'rev16 ${0:w}, ${1:w}'

Chromium compiled on the same host a couple of months ago, but the 
executable failed on a runtime library error. Now attempts to upgrade
stop during compilation. Ports are presently at revision 496949.

Thanks for reading, and any guidance.

bob prohaska