Fix armel tests build (dotnet/coreclr#24678)

Fix armel tests build (dotnet/coreclr#24678)

* Fix build-tests script for cross build and fix tests for armel

* Handle case of -skipcrossgen for cross builds

* Fix build error in case of cross builds when ROOTFS_DIR is not passed explicitly

* Fix portable build parameter setup for armel tests build

* Move force of non-portable build for armel from build.sh/build-test.sh to init-distro-rid.sh

* Fix priority1 tests build for armel

Commit migrated from https://github.com/dotnet/coreclr/commit/2e28c8114d58870ebc1ae8aac51b4539d2314452