Fix build on alpine-riscv64

[am11]

cc @viewizard @gbalykov

docker run --rm -v$(pwd):/diagnostics -w /diagnostics --platform linux/riscv64 alpine:edge sh -c \
  'apk add build-base cmake bash curl clang llvm-dev lldb-dev   &&   ./build.sh -skipmanaged'

[am11]

cc @shushanhf, LA64 can also use a port of libSOS to enable managed code debugging with lldb, see: https://github.com/dotnet/diagnostics/pulls?q=sort%3Aupdated-desc+is%3Apr+riscv64+is%3Aclosed.

[viewizard]

LGTM

[gbalykov]

cc @dotnet/samsung

[shushanhf]

cc @shushanhf, LA64 can also use a port of libSOS to enable managed code debugging with lldb, see: https://github.com/dotnet/diagnostics/pulls?q=sort%3Aupdated-desc+is%3Apr+riscv64+is%3Aclosed.

@am11 Thanks!
We are porting the related modules for LA64 and will push these.