AIX: fix compilation error because of missing <sstream>

Replace it by cmStandardIncludes.h which drags in the proper header depending
on what the compiler provides to fix this error:

CMake/Source/cmExtraCodeLiteGenerator.cxx:27: sstream: No such file or directory
Merge topic 'aix-no-sstream' into next

941a1404 AIX: fix compilation error because of missing <sstream>