It appears as if GhcEnableTablesNextToCode=NO breaks the NCG on macOS as early as GHC 8.4.

Running the following

git reset --hard HEAD
git clean -xfd
git submodule update --init --recursive
git clean -xfd
sed -E "s/^#BuildFlavour[ ]+= quick-cross$/BuildFlavour = quick/" < mk/build.mk.sample > mk/build.mk
echo "GhcEnableTablesNextToCode=NO" >> mk/build.mk
./boot && ./configure --silent && make -s -j9

on macOS with the 8.4 and 8.6 generated duplicate symbols in the assembly file.

Something like

.text
.align 3
Lc4l:
Lc4l:
        jmp Lc4u
.const_data
.align 3
.align 0
_Lc4l_info:
        .quad   Lc4l
        .quad   259
        .long   30
        .long   0

which causes the assembler to choke.