Quoting "The Open Group Base Specifications Issue 7" at
<http://pubs.opengroup.org/onlinepubs/9699919799/utilities/make.html#tag_20_76_13_01>
"Extended Description: Makefile Syntax:"  "When an escaped <newline> is found in
a command line in a makefile, the command line shall contain the <backslash>,
the <newline>, and the next line, except that the first character of the next
line shall not be included if it is a <tab>."

On Mac OS X, this caused raptor and rasqal to erroneously be configured with a
--prefix argument that ended in "--disable-static".

Change-Id: I9455f8e2e624b245a5278a21d8b0f62d8780f9e4