Support target specific ALIGN for variable alignment test [BZ #28676]

Add <tst-file-align.h> to support target specific ALIGN for variable
alignment test:

1. Alpha: Use 0x10000.
2. MicroBlaze and Nios II: Use 0x8000.
3. All others: Use 0x200000.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>