libsel4platsupport: don’t link nonexistent ltimers

If there is no ltimer for a particular platform, then these functions do not exist, so make the init_default_timer_ops() always return errors.

The intended way to avoid this is to not use the timer when CONFIG_LIB_PLAT_SUPPORT_NO_PLATFORM_LTIMER is set.

seL4 Libraries

A collection of libraries for working on seL4.

libsel4allocman: an allocator for managing virtual memory, malloc memory and cspaces.
libsel4bench: a library with utilities for benchmarking on seL4.
libsel4debug: a library with utilities for debugging on seL4. Only useful when debugging a userlevel app; potentially hacky.
libsel4muslcsys: a library to support muslc for the root task.
libsel4platsupport: a wrapper around libplatsupport specificially for seL4.
libsel4simple: an interface which abstracts over the boot environment of a seL4 application.
libsel4simple-default: an implementation of simple for the master branch of the kernel.
libsel4simple-experimental: an implementatoin of simple for the experimental branch of the kernel.
libsel4sync: a synchronisation library that uses notifications to construct basic locks.
libsel4test: a very basic test infrastructure library.
libsel4utils: a library OS - Commonly used stuff, actively maintained: implements threads, processes, elf loading, virtual memory management etc.
libsel4vka: an allocation interface for seL4.
libsel4vspace: a virtual memory management interface for seL4.