static call fixes for clang's conditional tail calls (6.2 and 6.1)

Hi Greg and Sasha,

Please consider applying the following commits to 6.2 (they apply cleanly with some fuzz for me):

db7adcfd1cec ("x86/alternatives: Introduce int3_emulate_jcc()") ac0ee0a9560c ("x86/alternatives: Teach text_poke_bp() to patch Jcc.d32 instructions") 923510c88d2b ("x86/static_call: Add support for Jcc tail-calls")

I have attached backports to 6.1.

Without these changes, kernels built with any version of clang using -Os or clang 17.0.0 (tip of tree) at any kernel-supported optimization level do not boot. This has been tested by people affected by this problem, see https://github.com/ClangBuiltLinux/linux/issues/1774 for more info.

If there are any problems, please let me know.

Cheers, Nathan