multiple definition of 'ghc_unique_counter64' when building 9.12.0.20241128 with 9.8.4

when I build ghc-9.12.0.20241128 from source, using ghc-9.8.4, I get

...
===> Command failed with error code: 1
/usr/bin/ld.gold: error: /usr/local/waldmann/opt/ghc/ghc-9.8.4/lib/ghc-9.8.4/lib/../lib/x86_64-linux-ghc-9.8.4/rts-1.0.2/libHSrts-1.0.2_thr.a(Globals.thr_o): multiple definition of 'ghc_unique_counter64'
/usr/bin/ld.gold: _build/stage0/lib/../lib/x86_64-linux-ghc-9.8.4-inplace/ghc-9.12.0.20241128-inplace/libHSghc-9.12.0.20241128-inplace.a(genSym.o): previous definition here
collect2: error: ld returned 1 exit status
`gcc' failed in phase `Linker'. (Exit code: 1)

it works when using 9.8.3, and also 9.10.1

added needs triage label

removed needs triage label

added Tbug backport needed:9.10 backport needed:9.12 backport needed:9.8 labels

We should add CPP guards to disable the definition in genSym.c with GHC 9.8.4, and GHC 9.6.7, which both include the 64-bit Unique refactor (!10568 (closed)).

This should be backported to %9.10.2, %9.12.2.

assigned to @bgamari

mentioned in commit e421ec3c

mentioned in merge request !13743 (closed)

mentioned in commit 956f8410

mentioned in commit 63d74f4d

mentioned in commit 72482a43

mentioned in commit 5415f266

mentioned in commit c5b146dc

closed with commit 595013d4

mentioned in commit 595013d4

mentioned in commit 058d661c

mentioned in commit 189a368b

mentioned in commit a7402f41

marked this issue as related to #25963

mentioned in commit 0dabd3c1

mentioned in commit 7494644f