Here are some instructions for building Gqrx 2.5.3 from source on FreeBSD.
These instructions have been tested on FreeBSD/amd64 10.2-RELEASE. Gqrx
mostly builds out of the box, with some minor adjustments shown below:

Gqrx uses ALSA audio by default. For some reason this didn't work for me,
and I had to convince it to use Pulseaudio instead. Normally it only wants
to use Pulseaudio on Linux. This can be changed as follows:

1) Edit the top-level CMakeLists.txt file and find the following line:

if(${CMAKE_SYSTEM_NAME} MATCHES "Linux")

Change it to:

if(${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD")

2) Edit src/CMakeLists.txt and find the following line:

elseif((${CMAKE_SYSTEM_NAME} MATCHES "Linux") AND (${LINUX_AUDIO_BACKEND} MATCHES "Pulseaudio"))

Change it to:

elseif((${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD") AND (${LINUX_AUDIO_BACKEND} MATCHES "Pulseaudio"))

Now configure and build Gqrx as follows:

% mkdir build
% cd build
% cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr/local/gqrx ..
% gmake VERBOSE=1
% gnake VERBOSE=1 install

Note that this will install Gqrx under /usr/local/gqrx to keep it from
conficting with the existing FreeBSD package.