Add missing common_sse2.h file to makefile.unix
Add missing common_sse2.h file to makefile.unix

This was missed in bf2b4f114f2358682fbea05a8066729dc2cb6f81

Change-Id: Ib0d2ac9f5b86196de2ac8feccbb9536530e991b2

webmproject/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp