I recently picked up the Pine H64 which has the Allwinner “H6” Quad-Core ARM Cortex A53 64-Bit Processor. How would I go about compiling Icecat in support for this on Manjaro ARM?
I've got no experience with manjaro myself, but not on the Pine itself; you always try to avoid building on the embedded device (building firefox on a A53 with 3 GB RAM and relatively slow storage, which you'd also need to use for swap, would take days if not longer; though it could be much worse, you could be trying to do this on a raspberry pi...; note that you'll need more RAM than 3 GB, so you would need to have fast storage on which you can put a swap partition).
To cite maintainers of embedded distros:
Friends don't let friends build on the embedded target.
Typically, you build software using a cross-build toolchain on a workstation PC or on a server. In some cases, the most effective way is instead running on a beefier ARM server (you can rent these minute-accurately) or on a virtual machine.
Since Manjaro hails from Arch, arch ARM's methods of cross-building packages apply just as well. To little surprise, they assume that if you're building something as massive as firefox, you'd want to have compile machines which you use for the job. This might just be a aarch64 virtual machine on your development desktop machine. Then, you distribute the compile jobs to this(these) machine(s) using distcc, and get a coffee, a shower, another coffee, lunch, a nap, then have a walk, call your mom, have tea and supper, and then check back on your compilation.
For comparison: Building that software on IBM's relatively well-equipped arm64 build machines takes more than 7 hours; and that was on a 5-CPU, 40 GB RAM, high-bandwidth Applied Micro X-Gene2 server with SATA or PCIe SSD storage. While your A53 really is a neat little CPU, which can do a lot per CPU clock cycle, the X-Gene2 has about twice as many "useful operations" per cycle, and software building tasks are typically also very RAM bandwidth intense, so you'd assume significantly more than a factor of two in speed for these kinds of tasks.
All in all: Especially in the browser landscape, I'd check twice whether someone has built a self-contained binary image for your machine; doesn't sound that unlikely!