[SystemZ] Fix regression in test macro-prefix-map-lambda.cpp

The failing test comes from https://reviews.llvm.org/D152570.
Root cause of the failure is that a string constant on SystemZ
has an alignment of 2, not 1. The CSKY target has a similar problem.
The solution is to replace the fixed number with a regex.

Reviewed By: uweigand, tuliom, Zibi

Differential Revision: https://reviews.llvm.org/D153352