This commit brings all the changes made by running gdb/copyright.py
as per GDB's Start of New Year Procedure.
For the avoidance of doubt, all changes in this commits were
performed by the script.
The ## marker tells automake to not include the comment in its
generated output, so use that in most places where the comment
only makes sense in the inputs.
These rules don't depend on the target compiler settings, so hoist
the build logic up to the common builds for better parallelization.
We leave the mips rules in place as they depend on complicated
arch-specific configure logic that needs to be untangled first.
