When calling make_indirect_call with a parameter which is known,
Clang, since the 18.x release, can end up producing a specialized
version of the function which omits the cfguard check call (as the
target is known) and calls the known target directly.
The function is marked with a noinline attribute, to avoid
the compiler optimizing out the cfguard check call when the
target is known, but even with a noinline function, the compiler
apparently can make a separate specialized version of it.
To avoid the compiler doing such optimizations, reference the
target function via a global variable - the compiler can't assume
anything about the contents of them (they could be altered between
initialization and reading them later).
This fixes the cfguard invalid_icall test with Clang 18.x, when
compiled with optimizations enabled.
Martin Storsjö