[R] Install with prebuilt libarrow binary fails at link time when libxml2 is missing #55252

Describe the bug, including details regarding any error messages, version, and platform.

Since 26.0.0 the prebuilt Linux libarrow binaries have Azure on, so configure adds -lxml2 to the link line:

The binary pre-check in nixlibs.R only tests for curl and openssl headers, so a machine without libxml2-dev downloads the binary and then fails linking arrow.so with cannot find -lxml2, rather than falling back to a source build. Reported by the r2u maintainer after clean Docker builds of 26.0.0 failed.

SystemRequirements in DESCRIPTION calls libxml2 "(optional)", which is only true for source builds.

Component(s)

R