Thanks to https://aur.archlinux.org/cgit/aur.git/tree/use-system-libs.patch?h=xemu
--- a/meson.build
+++ b/meson.build
@@ -1180,11 +1180,7 @@
 endif
 have_vhost_user_gpu = have_vhost_user_gpu and virgl.found() and opengl.found() and gbm.found()
 
-tomllib = static_library('tomlpp', sources: files('toml.cpp'),
-                         include_directories: 'tomlplusplus/include')
-toml = declare_dependency(compile_args: ['-DTOML_HEADER_ONLY=0'],
-                          include_directories: 'tomlplusplus/include',
-                          link_with: tomllib)
+toml = dependency('tomlplusplus')
 
 genconfig = declare_dependency(include_directories: 'genconfig')
 
--- a/ui/thirdparty/meson.build
+++ b/ui/thirdparty/meson.build
@@ -60,7 +60,7 @@
 libfpng = static_library('fpng', sources: 'fpng/fpng.cpp', cpp_args: libfpng_cpp_args)
 fpng = declare_dependency(include_directories: 'fpng', link_with: libfpng)
 
-json = declare_dependency(include_directories: 'json')
+json = dependency('nlohmann_json')
 httplib = declare_dependency(include_directories: 'httplib')
 
 libfatx = static_library('fatx', sources: 'fatx/fatx.c')
--- a/ui/xui/reporting.cc
+++ b/ui/xui/reporting.cc
@@ -24,7 +24,7 @@
 #include "reporting.hh"
 #define CPPHTTPLIB_OPENSSL_SUPPORT 1
 #include <httplib.h>
-#include <json.hpp>
+#include <nlohmann/json.hpp>
 using json = nlohmann::json;
 
 #define DEBUG_COMPAT_SERVICE 0