Following up #72078, on x86-64 this allows a global to be considered
small or large regardless of the code model. For example, x86-64's
medium code model by default classifies globals as small or large
depending on their size relative to -mlarge-data-threshold.
GPU compilations compile the same TU for both the host and device, but
only codegen the host or device portions of it depending on attributes.
However, we still Sema the TU, and will warn on an unknown attribute for
the device compilation since this attribute is target-specific. Since
they're intended for the host, accept but ignore this attribute for
device compilations where the host is either unknown or known to
support the attribute.
Co-authored-by: @pranavk
