build: upgrade to C++20

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Idf0639ef3e1f2bc464820f6d9c535c278840df4c
diff --git a/meson.build b/meson.build
index 92e23a7..f5d371c 100644
--- a/meson.build
+++ b/meson.build
@@ -4,14 +4,14 @@
     default_options: [
         'warning_level=3',
         'werror=true',
-        'cpp_std=c++17',
+        'cpp_std=c++20',
         'prefix=/usr',
         'b_lundef=false',
         'buildtype=debugoptimized',
     ],
     license: 'Apache-2.0',
     version: '1.0',
-    meson_version: '>=0.49.0',
+    meson_version: '>=0.57.0',
 )
 
 phosphor_logging = dependency('phosphor-logging')