[compiler-rt] Use portable "#!/usr/bin/env bash" shebang for tests.

In build_symbolizer.sh we can safely remove the -eu argument from the shebang (which is an unportable construct), as the scripts sets **-e** and **-u** already.

Differential Revision: https://reviews.llvm.org/D110039

GitOrigin-RevId: 626e2a6c6236d2fd7582928a0363d381c55eb43d