-Qunused-arguments makes completion timeout

[Sarcasm]

Discussion starts here: #3 (comment)

Original reporter: @soonhokong

With the following irony-cdb-menu output:

Compilation Database: irony-cdb-json

  Working Directory: /Users/soonhok/work/dReal3/build/debug-clang
  Compile Options:   -Wall -Wextra -std=c++11 -Wno-mismatched-tags -Qunused-arguments -stdlib=libc++ -g -DDREAL_DEBUG -DDREAL_TRACE -fno-inline -Iinclude -Iinclude/ibex -I/Users/soonhok/work/dReal3/src -I/Users/soonhok/work/dReal3/src/opensmt -I.

[q] to quit

Removing -Qunused-arguments makes the timeout disappear.