Enabling CONFIG_RD_ZSTD (which is enabled by default) resulted in a
link failure on ia64:

+ ld -r -o vmlinux.o --whole-archive arch/ia64/kernel/head.o init/built-in.a usr/built-in.a arch/ia64/kernel/built-in.a arch/ia64/mm/built-in.a kernel/built-in.a certs/built-in.a mm/built-in.a fs/built-in.a ipc/built-in.a security/built-in.a crypto/built-in.a block/built-in.a lib/built-in.a arch/ia64/lib/built-in.a lib/lib.a arch/ia64/lib/lib.a drivers/built-in.a sound/built-in.a net/built-in.a virt/built-in.a arch/ia64/pci/built-in.a arch/ia64/hp/common/built-in.a --no-whole-archive --start-group --end-group
ld: lib/zstd/entropy_common.o: linking constant-gp files with non-constant-gp files
ld: failed to merge target specific data of file lib/zstd/entropy_common.o
ld: lib/zstd/fse_decompress.o: linking constant-gp files with non-constant-gp files
ld: failed to merge target specific data of file lib/zstd/fse_decompress.o
ld: lib/zstd/zstd_common.o: linking constant-gp files with non-constant-gp files
ld: failed to merge target specific data of file lib/zstd/zstd_common.o

This is seen on Debian unstable, with gcc 10.2 and binutils 2.35.  A
full build log is available at:
https://buildd.debian.org/status/fetch.php?pkg=linux&arch=ia64&ver=5.9~rc4-1~exp1&stamp=1599955166&raw=1

Ben.

-- 
Ben Hutchings
Humour is the best antidote to reality.