misc: Implement alignof, alignas, noreturn and static_assert manually

The headers these constructs belong in were introduced with C11
standard library, but don't appear to be supported by the Arm Compiler
6's. We work around this by implementing them ourselves.

Change-Id: I601701c0a8e2b5df02e7c2c95c5b0667aac6cff4
Signed-off-by: Chris Kay <chris.kay@arm.com>