Compile libart.so and libart-compiler.so with 2MB section alignment.

Adds the appropriate linker flags for libart and libart-compiler to have
2MB section alignment. This allows the executable segment of these
libraries to be backed by transparent hugepages on supporting systems.

Bug: 158135888
Test: Verified ELF format

Change-Id: Ia6455418cf1fdd3a1a98d662bf381db4b58b8536