[Bug c/100483] Extend -fno-semantic-interposition to global variables

[i at maskray dot me via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100483

--- Comment #1 from Fangrui Song <i at maskray dot me> ---
Another request is a new option: -fno-semantic-interposition-function. With
this option, we only assume functions cannot be interposed.
-fno-semantic-interposition assumes both functions and variables cannot be
interposed.