Add build-many-glibcs.py arm-linux-gnueabihf-v7{-disable-multiarch}

This patch adds two extra configuration for arm-linux-gnueabihf to
cover for multiarch support:

  1. arm-linux-gnueabihf-v7a: enables multiarch support by using
     -march=armv7a.

  2. Same as 1. but with --disable-multiarch.

Check with build-many-glibcs.py for both options.

	* scripts/build-many-glibcs.py (Context.add_all_configs):
	Add arm-linux-gnueabihf multiarch extra_glibcs.