[llvm] [FileCheck] Improve printing variables with escapes (PR #145865)

[Thomas Preud'homme via llvm-commits]

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@@ -0,0 +1,17 @@
+; RUN: echo -e "WINPATH=A:\windows\style\path"             >  %t
+; RUN: echo -e "NOT_ESCAPED=shouldn't be escaped [a-Z]\+$" >> %t
+; RUN: echo -e 'ESCAPED=\\ needs\to "be" escaped\000'      >> %t
+
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RoboTux wrote:

Maybe add examples of:
- a numeric expression regex still being escaped (e.g. [[#%X]])
- a failed numeric expression substitution

https://github.com/llvm/llvm-project/pull/145865