Explain ifunc AArch64 woes a little more thoroughly.

Author: staticfloat

src/ccall.cpp

@@ -1492,9 +1492,11 @@ static jl_cgval_t emit_ccall(jl_codectx_t &ctx, jl_value_t **args, size_t nargs)
 #define is_libjulia_func(name) _is_libjulia_func((uintptr_t)&(name), #name)
 
     static jl_ptls_t (*ptls_getter)(void);
+    // directly accessing the address of an ifunc can cause compile-time linker issues
+    // on some configurations (e.g. AArch64 + -Bsymbolic-functions), so we guard the
+    // `&jl_get_ptls_states` within this `#ifdef` guard, and use a more roundabout
+    // method involving `jl_dlsym()` on Linux platforms instead.
 #ifdef _OS_LINUX_
-    // directly accessing the address of an ifunc can cause linker issue on
-    // some configurations (e.g. AArch64 + -Bsymbolic-functions).
     jl_dlsym(jl_dlopen(nullptr, 0), "jl_get_ptls_states", (void **)&ptls_getter, 0);
 #else
     ptls_getter = &jl_get_ptls_states;