[PATCH v2 00/13] Add static_call()

[Peter Zijlstra]

This series, which depends on the previous two, introduces static_call().

static_call(), is the idea of static_branch() applied to indirect function
calls. Remove a data load (indirection) by modifying the text.

These patches are still based on the work Josh did earlier, but incorporated
feedback from the last posting and have a lot of extra patches which resulted
from me trying to actually use static_call().

This still relies on objtool to generate the .static_call_sites section, mostly
because this is a natural place for x86_64 and works for both GCC and LLVM.
Other architectures can pick other means if/when they implement the inline
patching. The out-of-line (aka. trampoline) variant doesn't require this.