[compiler-rt][rtsan] Use sanitizer internal allocator during rtsan init to avoid segfault in dlsym (#98679)

Follows https://github.com/llvm/llvm-project/pull/98268 with a fix for a
segfault during preinit on `ubuntu:20.04` environments. Previously,
`rtsan` was not handling the situation where `dlsym` calls `calloc`
during the interceptors initialization, resulting in a call to a
function at a null address.

@cjappl and I took inspiration from the solution in `nsan`, but we
re-used the sanitizer internal allocator instead of our own static
buffer. This PR also re-enables the existing non-instrumented `rtsan`
tests for `x86_64` and `arm64` architectures.

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Co-authored-by: Chris Apple <cja-private@pm.me>

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