[vendor] Default to `:cflags` option for BS generation.
[vendor] Default to `:cflags` option for BS generation.

Fixes http://hipbyte.myjetbrains.com/youtrack/issue/RM-388.

HipByte/RubyMotion,katsuyoshi/RubyMotion,incbee/RubyMotion,jjaffeux/RubyMotion,jjaffeux/RubyMotion,incbee/RubyMotion,beni55/RubyMotion,HipByte/RubyMotion,hboon/RubyMotion,katsuyoshi/RubyMotion,katsuyoshi/RubyMotion,beni55/RubyMotion,incbee/RubyMotion,jjaffeux/RubyMotion,katsuyoshi/RubyMotion,jjaffeux/RubyMotion,beni55/RubyMotion,incbee/RubyMotion,HipByte/RubyMotion,hboon/RubyMotion,beni55/RubyMotion,hboon/RubyMotion