'asm/hwcap.h' file not found building chromium on Pi3

[bob prohaska]

Made another attempt to compile www/chromium on a Pi3B, this time using
a mechanical hard disk for all storage (and boot). It stopped with

../../third_party/zlib/cpu_features.c:32:10: fatal error: 'asm/hwcap.h' file not found
#include <asm/hwcap.h>
         ^~~~~~~~~~~~~
1 error generated.

Ports are at Revision: 537041, uname -a reports 12.1-STABLE r361429 
GENERIC  arm64. All make commands used -DBATCH.

Thanks for reading, any hints appreciated...

bob prohaska