sim: fix build error when glibc >= 2.34

Since glibc >= 2.34, MINSIGSTKSZ and SIGSTKSZ are no longer
constant on Linux. As a result, the definition
"fatalSigStack[2*SIGSTKSZ]" fails to be compiled.
Thus, we need to dynamically allocate it.

Change-Id: Ibccc367818483b9c94beda871d1d95367d1e8b04
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/53183
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed