Here are some instructions for building KiCad 4.0.2 from source on FreeBSD.
These instructions have been tested on FreeBSD/amd64 10.2-RELEASE. KiCad
mostly builds out of the box, with a few minor adjustments as shown below.

1) KiCad wants WxWidgets 3.0 and to run wx-config, but FreeBSD calls it
wxgtk2u-3.0-config. Create an alias, or make a symlink like this:

% ln -s /usr/local/bin/wxgtk2u-3.0-config wx-config
% setenv PATH `pwd`:$PATH

2) During the build, KiCad downloads the Boost source code and applies some
patches to it. The problem is the patches have Microsoft-style line breaks
in them (^M) which confuses the patch command a little. Go to the
kicad-4.0.2/patches directory and tweak all the .patch files to get rid of
the CTRL-Ms.

3) Update CMakeModules/download_boot.cmake so that it uses clang instead
of gcc:

--- download_boost.cmake.orig   2016-03-31 19:47:17.932416000 -0700
+++ download_boost.cmake        2016-03-31 19:47:24.940326000 -0700
@@ -92,7 +92,7 @@
 #message( STATUS "REPLACE libs_csv:${boost_libs_list}" )
 
 # Default Toolset
-set( BOOST_TOOLSET "toolset=gcc" )
+set( BOOST_TOOLSET "toolset=clang" )
 
 if( KICAD_BUILD_STATIC OR APPLE )
     set( BOOST_LINKTYPE  "link=static" )
@@ -130,7 +130,7 @@
     string( REGEX REPLACE "\\;" "," libs_csv "${boost_libs_list}" )
     #message( STATUS "libs_csv:${libs_csv}" )
 
-    set( bootstrap ./bootstrap.sh --with-libraries=${libs_csv} )
+    set( bootstrap ./bootstrap.sh --with-toolset=clang --with-libraries=${libs_csv} )
     # pass to *both* C and C++ compilers
     set( BOOST_CFLAGS   "cflags=${PIC_FLAG}" )
     set( BOOST_CXXFLAGS "cxxflags=${PIC_FLAG}" )

4) Sometimes kicad dumps core on exit. Fix  kicad-4.0.2/kicad/kicad.cpp:

--- kicad.cpp.orig      2016-03-31 23:10:10.622662000 -0700
+++ kicad.cpp   2016-03-31 23:10:36.885092000 -0700
@@ -278,6 +278,9 @@
 
         Pgm().OnPgmExit();
 
+        /* Avoid crash */
+        wxLog::EnableLogging(false);
+
         return wxApp::OnExit();
     }
 

5) Create a build/release path under the kicad-4.0.2 source directory, and then go there:

% cd /path/to/kicad-4.0.2
% mkdir build
% mkdir build/release
% cd build/release

6) Run cmake with the following command, where KICAD_SRC_DIR is the directory
where you unpacked kicad-4.0.2 (FreeBSD has its own potrace library which
conflicts with the one that's shipped with KiCad):

% cmake -DCMAKE_BUILD_TYPE=Release -DKICAD_SCRIPTING=ON \
	-DKICAD_SCRIPTING_MODULES=ON -DKICAD_SCRIPTING_WXPYTHON=ON \
	-DCMAKE_INSTALL_PREFIX=/usr/local/kicad4 \
	-DDEFAULT_INSTALL_PATH=/usr/local/kicad4 \
	-DCMAKE_C_FLAGS="-IKICAD_SRC_DIR//kicad-4.0.2/potrace -I/usr/local/include" \
	-DCMAKE_CXX_FLAGS="-IKICAD_SRC_DIR/kicad-4.0.2/potrace -I/usr/local/include" \
	-DKICAD_REPO_NAME=stable -DKICAD_BUILD_VERSION=4.0.2 ../../

Note that this uses /usr/local/kicad4 as the installation directory.

7) Do the build:

% gmake VERBOSE=1

8) Do the install:

% gmake VERBOSE=1 install