build(meson): simplify build options (#2176)

The "cpp-httplib_" prefix of build options is now dropped, as Meson
build options are already namespaced for each project. The old names
remain as deprecated aliases for the new ones.

meson.build

@@ -13,7 +13,7 @@ project(
     'b_lto=true',
     'warning_level=3'
   ],
-  meson_version: '>=0.62.0'
+  meson_version: '>=0.63.0'
 )
 
 cxx = meson.get_compiler('cpp')