Not every github Python project comes ready for use with pip/easy_install, but when you attempt to run it sometimes you'll quickly figure out the dependencies.

By running python app.py, from the initial errors it appears to depend on flask and weather-api, so this worked for me:

pip install --user flask weather-api
python app.py

Then it tells you to go to the local URL showing something like this:

The answers already provided do include all the necessary steps, just not in a single answer, so here goes (assumes you have already installed Git, which seems to be the case based on your question):

git clone https://github.com/vrai/fdspatch
cd fdspatch
make

This will report the warning about tempnam that you are already aware of, as stated elsewhere, this is a warning, not an error; the program will still run.

Let's prove the binary you have just built works, from the same fdspatch directory run:

./fdspatch

As we didn't provide any of the expected parameters, this will show the help file of the tool. If you're happy only being able to run this command from the fdspatch directory, there's no further action needed.

If you want to be able to run the fdspatch command from anywhere, you'll need to copy it to the systems binary directory (this IS documented on the project's github page, but the details are left to the reader...)

Assuming you're on the latest Raspberry Pi OS, this should work (again, assumes you are still in the fdspatch directory):

sudo cp fdspatch /usr/local/bin

You can then run the fdspatch command anywhere on the system.

All of the above has been tested and and shown to work on a RPi4 on latest Raspberryb Pi OS.

Not sure if this is helpful, but under the latest copy of Raspbian I was able to install RPi.GPIO directly from the main repositories using apt-get as follows:

sudo apt-get update
sudo apt-get -y install python-rpi.gpio

If you're running Python 3 (idle3 on the command line) instead of Python 2 (python on the command line) you need to install the RPi.GPIO library with this command instead:

sudo apt-get -y install python3-rpi.gpio

sudo apt-get install python3-pip

This should install pip3 for managing Python3 libraries. If you're using rasbian that is.
python-pip is for Python2 (as of 2019-09-09) if you need that too.

pip and python are two separate entities. There for installing one doesn't necessarily mean the other will be installed.

Some good documentation on the matter can be found at raspberrypi.org

And others have asked the same question on the official forums.

Just remember, most "safe" distro's tend to default to Python2 for their LTS platforms pre 2020. Meaning you will have to essentially add python3-<lib> (the 3 being the crucial element here) to all your installations. Otherwise you'll most likely get the Python2 equivilant of the library/tool for as long as Python2 is the default python environment in your distro. Like in this case.

Again, I'm using Arch Linux ARM for the most part, so I'm not to familiar with debian/ubuntu/etc distro's for the RPi platform. But that package should be called about the same as in Arch :)