Step 1)
Familiarise yourself with the concept and lisencing for GNU software:
https://en.wikipedia.org/wiki/GNU_Ge...Public_License

Step 2)
Become rightfully pissed off with Microchip for selling something they made
absolutely no contribution toward the creation of, and non-compiance with GNU
for deliberately introducing difficulties compiling source after anyone has done so.
The former, they have every right to do, although morally reprehensible, and not at
all in the spirit of open source software. The later is a blatant GNU lisence breach.

Step 3)
Download the current version of XC16 for Apple Mac OS, or Windows directly from Microchip.
The current XC16 is version 1.33. Install MPLAB-X and XC16 normally.

Step 4)
Locate in Windows:
C:\Program Files\Microchip\xc16\v1.33\bin\bin\elf-cc1.exe

Locate in Mac OS:
/Applications/microchip/xc16/v1.33/bin/bin/elf-cc1

Back up this orginal file somewhere.

Step 5)
Take what already belongs to you, which is specifically GCC (XC16/32).

Open the original file from it’s original location with any hex editor program.

For Windows:
Find file offset: 0x161E7E, and change the original value 0x85 to 0x84.

For Mac OS:
Find file offset: 0x64CCC7, and change the original value 0x85 to 0x84.

Save the file, and you now have the pro version with every level optimisation.
Free as it was intended by it’s actual authors, who see none of the $1000 Microchip ask.