Set default 'mips_arch_variant%' to 'r6'

With this change webrtc optimizations are excluded
for all mips32 arch variants.

This needs to be done as we have one gyp_webview target
for all mips32 arch variants and r6 doesn't support
a number of instructions which are supported in r1/r2.

This is a temp workaround until a better solution is found.

Change-Id: I10406245f9708b9eacc40af83549a79f021944c7
1 file changed