To reproduce with Emacs -Q: Open src/data.c and do M-x hide-ifdef-mode.

Should get you something like:

Debugger entered--Lisp error: (error "Bad token in parenthesized expression: 125")
   signal(error ("Bad token in parenthesized expression: 125"))
   error("Bad token in parenthesized expression: %s" 125)
   hif-factor()
   hif-math()
   hif-eq-expr()
   hif-and-expr()
   hif-or-expr()
   hif-expr()
   hif-parse-if-exp((lparen FLT_RADIX equal 2 and FLT_MANT_DIG equal 24 and FLT_MIN_EXP equal hif-minus 125 and FLT_MAX_EXP equal 128 rparen))
   hif-canonicalize()
   hif-possibly-hide()
   hide-ifdef-guts()
   hif-recurse-on(1351 1547)
   hif-possibly-hide()
   hide-ifdef-guts()
   hide-ifdefs()
   hide-ifdef-mode(toggle)
   call-interactively(hide-ifdef-mode)
   execute-extended-command(nil)
   call-interactively(execute-extended-command)

The bug occurs when `hif-factor' tries to parse the unary minus in:

#if (FLT_RADIX == 2 && FLT_MANT_DIG == 24 \
      && FLT_MIN_EXP == -125 && FLT_MAX_EXP == 128)

The attached, somewhat naive, patch fixes the bug for me.  Could someone
who uses `hide-ifdef-mode' on a regular basis check whether that fix
breaks something else.  Thanks in advance.