Since commit v3.1.0-rc1~635^2~7 (project: Add infrastructure for
recording CXX compiler features, 2013-10-17) we compile a test source to
a binary and then extract "<LANG>_FEATURES:..." strings from the binary
with the file(STRINGS) command.  Add a newline at the beginning of the
string literal to be sure file(STRINGS) can extract the first entry as a
string independent of whatever else the compiler may put before the
storage it allocates for the literal within the binary.