Is it possible to display compiler warnings in Arduino?

Using Arduino IDE 1.6.4 and newer, the warning level can be easily adjusted via menu File → Preferences → Compiler warnings:.

Using Arduino AVR Boards, the compiler flags set via this option are:

• "None": -w
• "Default":
• "More: -Wall
• "All": -Wall -Wextra

The default compiler command line options include -w, which suppresses warnings, but you can change that by editing C:\Program Files (x86)\Arduino\hardware\arduino\avr\platform.txt. Since the libraries might contain warnings, but I want -Werror for myself, I removed the -w options, and then added to my source code:

#pragma GCC diagnostic error "-Wall"
#pragma GCC diagnostic error "-Werror"

Most answers here seem to be outdated. From Arduino.app 1.5 onwards you must find the file preferences.txt (https://www.arduino.cc/en/Hacking/Preferences) and change the line compiler.warning_level=none to compiler.warning_level=all IMPORTANT: Quit Arduino first, edit, then start the IDE again.

The feature as described by Matthew, not only displays the warnings, but a lot of distracting information on how the compiler was called as well.

See the addendum to my question Have the Arduino IDE set compiler warnings to error. It implements the changes to the Arduino script:

-export PATH="${APPDIR}/java/bin:${PATH}"
+export ORGPATH="${APPDIR}/java/bin:${PATH}"
+export PATH="${APPDIR}/extra:${ORGPATH}"

And make the extra/avr-g++:

#! /usr/bin/env python

import os
import sys
import subprocess

checklibpat = [
    'SoftwareSerial',
    'GSM_GPRS',
]

werr = '-Werror'
wall = '-Wall'

cmd = ['avr-g++'] + sys.argv[1:]
os.environ['PATH'] = os.environ['ORGPATH']
fname = sys.argv[-2][:]
extend = False
warn = False
if cmd[-2].startswith('/tmp'):
    extend = True
    warn = True
if not extend:
    for l in checklibpat:
        if l in cmd[-2]:
            warn = True
            break
if warn:
    #print len(fname), list(fname)
    for i, c in enumerate(cmd):
        if c == '-w':
            cmd[i] = wall
            break
    if extend:
        cmd.insert(1, werr)
## to enable deprecated stuff (Print.cpp) with gcc 4.7.0
#cmd.insert(1, '-D__PROG_TYPES_COMPAT__=1')
subprocess.call(cmd)

Comment out extend = True if you do not want the compiler to interpret warnings in your source as errors.