11.4 Backslash-Newline-Newline in Make Macro Values
On some versions of HP-UX, make reads multiple newlines
following a backslash, continuing to the next non-empty line. For
FOO = one \
BAR = two
: FOO is "$(FOO)"
: BAR is "$(BAR)"
FOO equal to
one BAR = two. Other implementations
sensibly let a backslash continue only to the immediately following