Make PIE building/linking mandatory

[TheAssassin]

Future runtime types must be linked as PIE. Current ones should. This allows the kernel to apply ASLR and makes the runtime compatible with tools like https://github.com/io12/userland-execve-rust.

[probonopd]

Please elaborate the motivation for this. Especially why you think it should be a "must".

[TheAssassin]

See https://github.com/AppImage/type2-runtime/pull/88 for additional context. Using PIE is an advantage security wise (it allows the kernel to apply ASLR, non-PIC code cannot be loaded that way). Also, it allows the runtime to be launched via https://github.com/io12/userland-execve-rust, which is a convenient way for tools like AppImageLauncher to launch statically linked runtimes while bypassing binfmt_misc. It doesn't cost anything either and should be possible with any modern compiler toolchain.