Removing __linux__ definition in CMake

Removing this definition as this should already be defined by compiler.
This is causing compile errors on newer versions of llvm because the
macro is being redefined.

Change-Id: I3bf03617970d4b76dabce36ed980523673afadc5

CMakeLists.txt

@@ -123,7 +123,6 @@ if(${BUILD_TYPE} STREQUAL "Debug")
 add_definitions(-DDEBUG)
 endif()
 
-add_definitions(-D__linux__)
 add_definitions(-DLITTLEENDIAN_CPU=1)
 
 #