lib: c: re-organise into separate static modules, plus a single shared library

lib/libc/core/CMakeLists.txt

@@ -1,4 +1,4 @@
-set(source_dirs stdio string)
+set(source_dirs stdio string errno)
 
 foreach (dir ${source_dirs})
 	file(GLOB dir_sources ${CMAKE_CURRENT_SOURCE_DIR}/${dir}/*.c)
@@ -21,3 +21,5 @@ sysroot_add_library(
 	NAME libc-core
 	HEADER_DIR /usr/include
 	LIB_DIR /usr/lib)
+
+target_link_libraries(libc-core libmango)