Test pseudo-namespaces in C

In C you can create pseudo-namespaces by abusing structs of function
pointers, making function calls look like `module.func(x)` instead of
`func(x)`.

A lot of people online spout that this creates overhead, but this should
show that clang>=15.0.7 will still inline such function calls. GCC 11.3.1
is unable  to inline the function, but will still call the function
directly.

CMakeLists.txt

@@ -0,0 +1,20 @@
+
+cmake_minimum_required(VERSION 3.13)
+
+project(Namespaces)
+
+add_executable(main
+    module.c
+    main.c)
+
+target_compile_options(main
+	PRIVATE
+	-Werror -Wall -Wextra -O3 -g -std=c2x -flto)
+
+target_link_options(main
+	PRIVATE
+	-flto -Wl,-O2)
+
+target_compile_definitions(main
+	PRIVATE
+	-DNAMESPACES)