[libc] Build the `libc` objects using a generic AMDGPU ABI (#65782)

Summary:
AMDGPU binaries use a "code object" as the ABI indicator. We are
currently trying to move over to a newer code object. We want these
library functions to use the "generic" or default ABI such that it is
specified when linked into the user application. Currently this will
default to v4 as the startup code will use whatever the current default
is.