error: instruction requires: armv6t2 on RPI2

[bob prohaska]

In trying to compile www/firefox on RPI2 at r322520 using 

make -DBATCH CFLAGS='-mcpu=cortex-a7' > make.log

the system reports 
 error: instruction requires: armv6t2
  sbfx r8, r6, #12, #16
  ^
.....

Is there a workaround?  "armv6t2" does not seem to be a  recognized 
cpu type in clang5. 


Thanks for reading,

bob prohaska