The new line in the set(CMAKE_CXX_FLAGS...) line was getting insert
verbatim into the Makefile. Makefiles don't like new lines in their
assignment operators.

The newline escape fix works for CMake 3.0 and above, but since
we support 2.x, we need to use the legacy solution, which is to
split into two separate statements.

Tested: cmake -G"Unix Makefiles" works now on Mac.
Change-Id: I6f4655981b85087c4760c3d26ed0c97c4469ba93