new C preprocessor breaks nhc's build process

bash-2.03$ cat old
infix 5 \\

bash-2.03$ cat -vet old
infix 5 \\ $
$
bash-2.03$ cat new
infix 5 \\ --

bash-2.03$ cpp-2.95 old
# 1 "old"
infix 5 \\

bash-2.03$ cpp-2.95 new
# 1 "new"
infix 5 \\ --

bash-2.03$ cpp-3.4.1 old
# 1 "old"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "old"
old:1:10: warning: backslash and newline separated by space
infix 5 \
bash-2.03$ cpp-3.4.1 new
# 1 "new"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "new"
infix 5 \\ --
bash-2.03$

The new behavior is documented in cpp.info of the gcc-3.4.1 distribution.
Line 153 of nhc98-1.16/src/libraries/base/Data/List.hs
expects the old behavior.