[PATCH] [arm] Implement ARM .arch directive.

[Logan Chien]

  Hi Richard,

  Sorry for the late reply.

  IMO, this won't be a problem because the ARMAsmPrinter will emit .eabi_attribute directives, which has higher priority than the .arch directives.  The default value generated by ARMAsmPrinter will not be overwritten by ARMTargetELFStreamer.  You can imagine that the default value provided by .arch directive is only a fall-back if such attribute has not be set.  Besides, the ARMAsmPrinter is not generating the .arch directive at the moment.  My main purpose to write this patch is to support more directives so that we can enable integrated-as for ARM in the future.

  * For the .arch directive question, I have tried the `arm-linux-gnueabi-as`, the command line option (-march) will be ignored if the assembly file contains .arch directive.

  * For the GCC question, AFAIK, GCC will not generate the build attribute if the value is zero.

  Thanks for your comment.  Feel free to ask further question if my explanation is not clear.

  Logan

http://llvm-reviews.chandlerc.com/D2133

BRANCH
  arm-add-arch-directive

ARCANIST PROJECT
  llvm