wxwidgets: fix compile errors with clang

Disabled precompiled headers to fix build.

Fixes #22124.
Closes #22197.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
gromacs 4.6.3

Closes #21989.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
wine: fix building without x11

Closes #21986.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
irssi: requires clt

Closes #20952.
calc: use Homebrew's cc and appropriate OS X SDK

Fixes #22015.
cassandra 1.2.9

Closes #22223.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
quassel 0.9

Closes #22220.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
Fix wrong assumption in MacOS::Xcode.without_clt?

Fixes #22221.
Use system path for more tools, for Linux compat.

Closes #22196.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
libftdi 1.0

Closes #21758.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
apt-cacher-ng 0.7.18

Closes #22227.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
Show list of dependencies prior to installing them

Closes #22205.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
Remove PATH hack from ENV.fortran
Analog 6.0

Closes #21477.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
SDL2_net 2.0.0

Closes #22225.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
Simplify handling custom FCFLAGS
lnav 0.6.0

Closes #22228.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
ENV: add cc and cxx setters
ENV: use cc accessor
ENV: use cflags setter