[Patch] testsuite: Avoid TCL errors when ASAN/TSAN/UBSAN is not available

[Tobias Burnus]

In a --disable-libsanitizer build, I see errors such as:
   g++.sum:ERROR: can't read "asan_saved_library_path": no such variable

I believe the following patch is the right way to solve this.
OK?

Tobias

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