Use find_package to search for system lz4 before vendoring

Builds/CMake/deps/Findlz4.cmake

@@ -0,0 +1,22 @@
+find_package (PkgConfig REQUIRED)
+pkg_search_module (lz4_PC QUIET liblz4>=1.8)
+
+if(static)
+  set(LZ4_LIB liblz4.a)
+else()
+  set(LZ4_LIB lz4)
+endif()
+
+find_library (lz4
+  NAMES ${LZ4_LIB}
+  HINTS
+    ${lz4_PC_LIBDIR}
+    ${lz4_PC_LIBRARY_DIRS}
+  NO_DEFAULT_PATH)
+
+find_path (LZ4_INCLUDE_DIR
+  NAMES lz4.h
+  HINTS
+    ${lz4_PC_INCLUDEDIR}
+    ${lz4_PC_INCLUDEDIRS}
+  NO_DEFAULT_PATH)

Builds/CMake/deps/Libarchive.cmake

@@ -73,7 +73,7 @@ ExternalProject_Add (libarchive
       >
   TEST_COMMAND ""
   INSTALL_COMMAND ""
-  DEPENDS lz4
+  DEPENDS lz4_lib
   BUILD_BYPRODUCTS
     <BINARY_DIR>/libarchive/${ep_lib_prefix}archive${lib_post}${ep_lib_suffix}
     <BINARY_DIR>/libarchive/${ep_lib_prefix}archive${lib_post}_d${ep_lib_suffix}

Builds/CMake/deps/Lz4.cmake

@@ -2,7 +2,23 @@
    NIH dep: lz4
 #]===================================================================]
 
-ExternalProject_Add (lz4
+add_library (lz4_lib STATIC IMPORTED GLOBAL)
+
+if (NOT WIN32)
+  find_package(lz4)
+endif()
+
+if(lz4)
+  set_target_properties (lz4_lib PROPERTIES
+    IMPORTED_LOCATION_DEBUG
+      ${lz4}
+    IMPORTED_LOCATION_RELEASE
+      ${lz4}
+    INTERFACE_INCLUDE_DIRECTORIES
+      ${LZ4_INCLUDE_DIR})
+
+else()
+  ExternalProject_Add (lz4
     PREFIX ${nih_cache_path}
     GIT_REPOSITORY https://github.com/lz4/lz4.git
     GIT_TAG v1.8.2
@@ -39,21 +55,24 @@ ExternalProject_Add (lz4
     BUILD_BYPRODUCTS
       <BINARY_DIR>/${ep_lib_prefix}lz4${ep_lib_suffix}
       <BINARY_DIR>/${ep_lib_prefix}lz4_d${ep_lib_suffix}
-)
+  )
-ExternalProject_Get_Property (lz4 BINARY_DIR)
+  ExternalProject_Get_Property (lz4 BINARY_DIR)
-ExternalProject_Get_Property (lz4 SOURCE_DIR)
+  ExternalProject_Get_Property (lz4 SOURCE_DIR)
-if (CMAKE_VERBOSE_MAKEFILE)
+
-  print_ep_logs (lz4)
+  file (MAKE_DIRECTORY ${SOURCE_DIR}/lz4)
-endif ()
+  set_target_properties (lz4_lib PROPERTIES
-add_library (lz4_lib STATIC IMPORTED GLOBAL)
-file (MAKE_DIRECTORY ${SOURCE_DIR}/lz4)
-set_target_properties (lz4_lib PROPERTIES
     IMPORTED_LOCATION_DEBUG
       ${BINARY_DIR}/${ep_lib_prefix}lz4_d${ep_lib_suffix}
     IMPORTED_LOCATION_RELEASE
       ${BINARY_DIR}/${ep_lib_prefix}lz4${ep_lib_suffix}
     INTERFACE_INCLUDE_DIRECTORIES
       ${SOURCE_DIR}/lib)
+
+  if (CMAKE_VERBOSE_MAKEFILE)
+    print_ep_logs (lz4)
+  endif ()
+endif()
+
 add_dependencies (lz4_lib lz4)
 target_link_libraries (ripple_libs INTERFACE lz4_lib)
 exclude_if_included (lz4)

Builds/CMake/deps/Rocksdb.cmake

@@ -84,7 +84,7 @@ ExternalProject_Add (rocksdb
   LIST_SEPARATOR ::
   TEST_COMMAND ""
   INSTALL_COMMAND ""
-  DEPENDS snappy lz4
+  DEPENDS snappy lz4_lib
   BUILD_BYPRODUCTS
     <BINARY_DIR>/${ep_lib_prefix}rocksdb${ep_lib_suffix}
     <BINARY_DIR>/${ep_lib_prefix}rocksdb_d${ep_lib_suffix}

CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required (VERSION 3.9.0)
-list(APPEND CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/Builds/CMake)
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/Builds/CMake")
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/Builds/CMake/deps")
 
-set (CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/Builds/CMake ${CMAKE_MODULE_PATH})
 include (CheckCXXCompilerFlag)
 if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.11)
   include (FetchContent)