Quick Steps to build the decomps on a clean Windows OS

Note #1: For the sake of easiness, we'll install everything in their default paths, so C:\devkitPro and C:\Cygwin64.
Note #2: Win Key + R > inetcpl.cpl and make sure to check SSL 2.0, TLS 1.1 and TLS 1.2 to avoid getting errors.

1) Download and install devkitPro from here: https://github.com/devkitPro/installer/releases
2) Download and run the Cygwin installer from here: https://www.cygwin.com/install.html
   Inside the Cygwin installer do Next, Next, Next until you reach the Package Selection.
3) Set "View" to Full so you can look up any package that Cygwin has, and using the Search Bar, make sure to check these:
* gcc-core (Description: "GNU Compiler Collection (C, OpenMP)")
* gcc-g++ (Description: "GNU Compiler Collection (C++)")
* git (Description: "Distributed version control system")
* libpng-devel (Description: "PNG library")
* make (Description: "The GNU version of the 'make' utility")
4) Click on Next, let Cygwin handle the rest and close the installer once it's done.
5) Open up C:\cygwin64\Cygwin.bat at least once.
6) On Cygwin.bat type in these commands one by one:
* export DEVKITPRO=/opt/devkitPro
* echo "export DEVKITPRO=$DEVKITPRO" >> ~/.bashrc
* export DEVKITARM=$DEVKITPRO/devkitARM
* echo "export DEVKITARM=$DEVKITARM" >> ~/.bashrc
7) Time to clone agbcc and the desired decomp. For this demonstration, I'll use Pokeemerald.
* git clone https://github.com/pret/agbcc
* git clone https://github.com/pret/pokeemerald
8) Once they're done, we'll build Agbcc by doing:
* cd agbcc
* ./build.sh
9) Then we'll install Agbcc on our repository by doing:
* ./install.sh ../pokeemerald
10) And then we're ready to compile Pokeemerald by doing:
* cd ../pokeemerald
* make -jN
Note: "N" stands for the number of CPU Threads you want to assign to the compiler. The more threads, the faster it'll go.

And that's pretty much it.

If nothing went wrong, this should be the result: https://i.imgur.com/FOoCKTu.png