Add nlohmann dependency

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I8b0a1c01d05b053fc0669f626a975f406d88549a
diff --git a/src/rde/meson.build b/src/rde/meson.build
index 1f13f18..5cc45cf 100644
--- a/src/rde/meson.build
+++ b/src/rde/meson.build
@@ -1,6 +1,21 @@
+
+cpp = meson.get_compiler('cpp')
+if cpp.has_header('nlohmann/json.hpp')
+    nlohmann_json_dep = declare_dependency()
+else
+    subproject('nlohmann', required: false)
+    nlohmann_json_dep = declare_dependency(
+        include_directories: [
+            'subprojects/nlohmann/single_include',
+            'subprojects/nlohmann/single_include/nlohmann',
+        ]
+    )
+endif
+
 rde_pre = declare_dependency(
   include_directories: [rde_inc],
   dependencies: [
+    nlohmann_json_dep,
     dependency('libbej'),
     dependency('phosphor-dbus-interfaces'),
     dependency('sdbusplus'),