[analyzer] SARIF: Add EOF newline; replace diff_sarif

Summary:
This patch applies a change similar to rC363069, but for SARIF files.

The `%diff_sarif` lit substitution invokes `diff` with a non-portable
`-I` option. The intended effect can be achieved by normalizing the
inputs to `diff` beforehand. Such normalization can be done with
`grep -Ev`, which is also used by other tests.

Additionally, this patch updates the SARIF output to have a newline at
the end of the file. This makes it so that the SARIF file qualifies as a
POSIX text file, which increases the consumability of the generated file
in relation to various tools.

Reviewers: NoQ, sfertile, xingxue, jasonliu, daltenty, aaron.ballman

Reviewed By: aaron.ballman

Subscribers: xazax.hun, baloghadamsoftware, szepet, a.sidorin, mikhail.ramalho, Szelethus, donat.nagy, dkrupp, Charusso, jsji, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D62952

llvm-svn: 363822