Log Message:
postgresql*: explicitly mark BROKEN on Alpha

Support for Alpha was removed in 2014. This removed the spinlock and
memory barrier implementations, meaning Postgresql on Alpha no longer
compiles cleanly with the default options. According to the commit
message the code was "unlikely to currently work correctly".

Enthusiasts may wish to re-add Alpha support, but it should likely
only be done with proper testing to avoid data loss in the case someone
uses it.