Add libelfin submodule
MODIFY
.gitmodules
.gitmodules
[submodule "external/ELFIO"]
path = external/ELFIO
url = https://github.com/serge1/ELFIO
+[submodule "external/libelfin_cmake/libelfin"]
+ path = external/libelfin_cmake/libelfin
+ url = https://github.com/aclements/libelfin

ADD
external/libelfin_cmake/libelfin
+Subproject commit 946dde57e5caef8297b9339f3a7971401d540840

Add libelfin submodule