[test][llvm-dwarfdump] Add extra test case for invalid MD5 form

A subsequent patch will change how an invalid file name table is handled
to allow parsing to continue. This patch adds a test case that will
demonstrate a difference in behaviour with that change between invalid
file tables where the error is before the end of the stated prologue
length and where the error occurs after the stated length.

Reviewed by: dblaikie

Differential Revision: https://reviews.llvm.org/D72157