build: move src/nvim/xdiff to src/xdiff

Closes #11239

src/nvim/CMakeLists.txt

@@ -87,8 +87,8 @@ file(MAKE_DIRECTORY ${LINT_SUPPRESSES_ROOT}/src)
 
 file(GLOB NVIM_SOURCES *.c)
 file(GLOB NVIM_HEADERS *.h)
-file(GLOB XDIFF_SOURCES xdiff/*.c)
-file(GLOB XDIFF_HEADERS xdiff/*.h)
+file(GLOB XDIFF_SOURCES ../xdiff/*.c)
+file(GLOB XDIFF_HEADERS ../xdiff/*.h)
 
 foreach(subdir
         os

src/xdiff/xdiff.h

@@ -119,7 +119,7 @@ typedef struct s_bdiffparam {
 	long bsize;
 } bdiffparam_t;
 
-#include "../memory.h"
+#include "../nvim/memory.h"
 
 #define xdl_malloc(x) xmalloc((x))
 #define xdl_free(ptr) xfree(ptr)