#if: wrong macro usage for macros defined before the #if #720

When a macro that is already defined is used in #if / #elif, the reported MacroUsage is wrong.

#define X 1
#if defined(X)
#endif

Expected: one use of X at line 2, col 13.
Actual: no usage is reported.

#define X 1
#if X
#endif

Expected: one use of X at line 2, col 5.
Actual: the same use is reported twice.