Adjust CMakeLists.txt to use system-provided mmg and yaml-cpp libraries.

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b11c5ba..702423e 100755
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -122,28 +122,8 @@ if(MMG_MESH)
   add_definitions(-DMMG_MESH)
 
   # MMG
-  set(MMG_PREFIX mmg3d)
-  set(MMG_PREFIX_DIR ${CMAKE_CURRENT_BINARY_DIR}/${MMG_PREFIX})
-  set(MMG_INSTALL_DIR ${CMAKE_CURRENT_BINARY_DIR}/${MMG_PREFIX})
-  ExternalProject_Add(${MMG_PREFIX}
-    PREFIX       ${MMG_PREFIX_DIR}
-    SOURCE_DIR   ${CMAKE_CURRENT_SOURCE_DIR}/libs/mmg
-
-    BUILD_ALWAYS OFF
-    INSTALL_DIR  ${MMG_INSTALL_DIR}
-
-    CMAKE_ARGS(-DCMAKE_BUILD_TYPE=Release -DBUILD=MMG3D -DLIBMMG3D_STATIC=ON
-               -DLIBMMG3D_SHARED=OFF -DCMAKE_INSTALL_PREFIX=<INSTALL_DIR>)
-
-    BUILD_COMMAND   make
-    INSTALL_COMMAND make install
-  )
-  set(MMG3D_INCLUDE_DIRS "${MMG_INSTALL_DIR}/include")
-  set(MMG3D_LIBRARIES "${MMG_INSTALL_DIR}/${CMAKE_INSTALL_LIBDIR}/${CMAKE_STATIC_LIBRARY_PREFIX}${MMG_PREFIX}${CMAKE_STATIC_LIBRARY_SUFFIX}")
-
-  include_directories(${MMG3D_INCLUDE_DIRS})
-  #add_library(MMG3D STATIC IMPORTED)
-  #set_target_properties(MMG3D PROPERTIES IMPORTED_LOCATION "${MMG3D_LIBRARIES}")
+  include_directories(${MMG_INCLUDE_DIR})
+  set(MMG3D_LIBRARIES ${MMG_LIBRARY_DIR}/libmmg3d.so)
 
   # MshMet
   set(MSHMET_PREFIX mshmet)
@@ -192,14 +172,8 @@ target_include_directories(tet PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/libs/tetgen)
 target_compile_definitions(tet PUBLIC TETLIBRARY) # -DTETLIBRARY: flag to compile tetgen as a library
 
 # yaml
-file(GLOB yaml_SRC CONFIGURE_DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/libs/yaml/src/*.cpp) # Using file GLOB is not recomended!
-add_library(yaml STATIC)
-target_include_directories(yaml
-  PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/libs/yaml/include 
-  PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/libs/yaml/src
-)
-target_sources(yaml PRIVATE ${yaml_SRC})
-set_target_properties(yaml PROPERTIES CXX_STANDARD 11)
+find_package(yaml-cpp REQUIRED)
+include_directories(${YAML_CPP_INCLUDE_DIRS})
 
 # Compile options for debuging
 if(CMAKE_BUILD_TYPE MATCHES Debug)
@@ -259,7 +233,7 @@ if(MARCH_NATIVE)
 endif()
 
 # Create entries for C++ files in "ASLI" routine
-target_link_libraries(ASLI PUBLIC alg tet yaml)
+target_link_libraries(ASLI PUBLIC alg tet ${YAML_CPP_LIBRARIES})
 if(NOT MSVC)
   target_link_libraries(ASLI PUBLIC stdc++fs)
 endif()
@@ -272,7 +246,7 @@ if(CGAL_MESH)
 endif()
 
 if(MMG_MESH)
-  add_dependencies(ASLI ${MMG_PREFIX} ${MSHMET_PREFIX})
+  add_dependencies(ASLI ${MSHMET_PREFIX})
   target_link_libraries(ASLI PUBLIC ${MMG3D_LIBRARIES} ${MSHMET_LIBRARIES})
   if(SCOTCH_FOUND)
     target_link_libraries(ASLI PUBLIC ${SCOTCH_LIBRARIES} scotch)