The size of arrays is unsigned

[tautschnig]

Arrays have an unsigned size, and this must also be true when converting
string constants to arrays. Using signed size types resulted in
invariant failures in the simplifier, which were triggered by passing in
arrays with a negative size. Observed on several SV-COMP benchmarks in
the device drivers category, for example (with --unwind 2):
ldv-linux-3.16-rc1/43_2a_bitvector_linux-3.16-rc1.tar.xz-43_2a-drivers--net--wireless--iwlwifi--iwlwifi.ko-entry_point.cil.out.i

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[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: 6b5d608).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/113357598