Function $(switch ...) cannot be spread out over several lines

[cspiel]

The GNUMake-syntax function $(switch ...) cannot be spread out over several lines
with line-continuation operators.

en = green
se = $(switch $(en), \
       black, svart, \
       red, röd, \
       green, grön, \
       blue, blå, \
       white, vit)

# Bug: $(se) is empty; neither error, nor warning from omake(1).
println($"spread-out function: '$(en)', en -> '$(se)', se")

The author is well aware of the OMake-syntax (multi-line) version of the
switch function, but does not like to be surprised by his make
system. IMHO, either $(switch ...) should complain about the line
continuations or work as the multi-line version.