autoconf: Backslash-Newline Comments

1 
1 12.5 Backslash-Newline in Make Comments
1 =======================================
1 
1 According to Posix, Make comments start with `#' and continue until an
1 unescaped newline is reached.
1 
1      $ cat Makefile
1      # A = foo \
1            bar \
1            baz
1 
1      all:
1              @echo ok
1      $ make   # GNU make
1      ok
1 
1 However this is not always the case.  Some implementations discard
1 everything from `#' through the end of the line, ignoring any trailing
1 backslash.
1 
1      $ pmake  # BSD make
1      "Makefile", line 3: Need an operator
1      Fatal errors encountered -- cannot continue
1 
1 Therefore, if you want to comment out a multi-line definition, prefix
1 each line with `#', not only the first.
1 
1      # A = foo \
1      #     bar \
1      #     baz
1