C API demo for inference. (#7151)

demo/c-api/inference/CMakeLists.txt

@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 3.13)
+project(inference-demo LANGUAGES C VERSION 0.0.1)
+find_package(xgboost REQUIRED)
+
+# xgboost is built as static libraries, all cxx dependencies need to be linked into the
+# executable.
+if (XGBOOST_BUILD_STATIC_LIB)
+  enable_language(CXX)
+  # find again for those  cxx libraries.
+  find_package(xgboost REQUIRED)
+endif(XGBOOST_BUILD_STATIC_LIB)
+
+add_executable(inference-demo inference.c)
+target_link_libraries(inference-demo PRIVATE xgboost::xgboost)