LTO allows the compiler to prove variable values that non-LTO mode
cannot prove. The workaround for the gcc-7 __builtin_constant_p
quirk incorrectly caused LTO on older gcc to report __builtin_constant_p
as unsupported. Fix this by adding a stub asm() statement to hide the
value of the input parameter from the compiler.
Fixes: 1ed7cec714 ("Tighten __builtin_constant_p check to handle gcc-7")