Merge pull request #15878 from ethereum/find_fmt

Adds find_package for fmtlib, range-v3, nlohmann_json

Author: clonker

CMakeLists.txt

@@ -61,6 +61,11 @@ if (NOT IGNORE_VENDORED_DEPENDENCIES)
   include(fmtlib)
   include(nlohmann-json)
   include(range-v3)
+else ()
+  message(WARNING "-- Ignoring vendored dependencies. Will use installed versions if found. Versions may differ from the ones the compiler was tested with. Make sure to run the test suite and thoroughly test the resulting binaries before using them in production.")
+  find_package(fmt REQUIRED)
+  find_package(nlohmann_json REQUIRED)
+  find_package(range-v3 REQUIRED)
 endif()
 
 find_package(Threads)