Fix OpenMP test failing at ci.debian.net

Reshabh Sharmarequested to merge
reshabh-guest/llvm-toolchain:openmp-autopkgtest-fix into 7

/bin/sh echo was not ignoring backslash escapes even with -E

https://ci.debian.net/data/autopkgtest/unstable/amd64/l/llvm-toolchain-7/998991/log.gz

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