refactor(test): use static_assert (C++11)

[e-kwsm]

• test: remove C files
• refactor(test): use static_assert (C11, C++11)

preprocessor/doc/title.html

Lines 16 to 23 in d899a71

	<div>The library requires that the compiler supports <a
	href="topics/variadic_macros.html">variadic macros</a>. Since
	variadic macros are a C99 or C++11 feature the library ostensibly
	requires at least compilation at those C or C++ standard levels. A
	number of compilers support variadic macros at a lower level, so
	it still may be possible using the library at that compilation
	level, as long as strict C++98/C++03 compliance is not enforced.<br>
	</div>

Therefore static_assert is usable.