Change mips64 default to mips64r6 from mips64r2

Also add back mips flags previously can't be handled by clang

See aosp/build
  13066a8d4c2f8ddb2348e6d3df3948a0f4dbf105
  10326b3d7f1966381812ef55478619f714917c23

Change-Id: Iedc8dadd24f72fbd9c5589eec34677c1827290f3
4 files changed