[Linux] Add support for PCK embedding section with non GNU-ld linkers.

[bruvzg]

Fixes #87438

Replaces linker scripts with section data definition in the code (same as used on Windows), this seems to work with mold and lld (including LTO builds).

[akien-mga]

Looks good to me.

[Riteo]

I don't have much experience with linking so TIWAGOS but this looks like a win overall.

FTR, mold has some reasoning behind the absence of linker script support:

Mold supports a very limited set of linker script features, which is just sufficient to read /usr/lib/x86_64-linux-gnu/libc.so on Linux systems (on Linux, that file is contrary to its name not a shared library but an ASCII linker script that loads a real libc.so file.)

Beyond that, we have no plan to support any additional linker script features. The linker script is an ad-hoc, over-designed, complex language which we believe needs to be replaced by a simpler mechanism. We have a plan to add a replacement for the linker script to mold instead.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 3.6.