Vendorkernel related adjustments for making GCC8 the default compiler

Here are three independent commits, that build upon each other. I won't squash them. The kernel compiles, I'll test if it boots and then merge this together with the pmbootstrap aportgen changes (MR in the works). Afterwards, #103 (closed) can finally be closed 🎉

add shared patches folder for gcc8 compatibility

This introduces a new .shared-patches folder. New "pmbootstrap aportgen" code will make use of this, and create symlinks to the patches inside that folder when running "pmbootstrap aportgen linux-..." (or using the new device wizard).

devicepkg-dev: ship compiler-gcc.h for GCC8

We used to put a "compiler-gcc6.h" file inside every vendor kernel's aport. This is redundant and only works with GCC6. With this patch, a common "compiler-gcc.h" file will be used, that works independently of the GCC version.

The file is from @ryang2678's android_kernel_samsung_p4 repository, where it was taken from upstream Linux, but adjusted to work with older vendor kernels (different #ifndef check at the top etc).

https://github.com/Decatf/android_kernel_samsung_p4/blob/bd0772df2132bf56cda78e7204facf434cd5aa40/include/linux/compiler-gcc.h

linux-lg-mako: modernize with new gcc8 linux aportgen code

regenerated the aport as proof of concept

(please do not squash!)

Fixes #103 (closed), closes #95 (closed).