bootloader & kernel: Build zlib with -Wno-error=missing-prototypes.

Will be needed for some newer zlib versions.

Switch package kit to BZlibCompressionAlgorithm

... and remove the Zlib{Compressor,Decompressor} API.

2nd attempt at fixing build of btrfs and packagefs.

* adding zlib to the kernel unfortunately introduces a cyclic dependency
with respect to the zlib, haiku and haiku_devel packages (AFAICS)
* circumvent this by building kernel_zlib as a static library again,
this time with PIC, such that it can be used by kernel add-ons

Revert "Fix build problems of btrfs and packagefs for x86_64."

This reverts commit f272e63f393449d3a816970ca632764895a78cd6.

Fix build problems of btrfs and packagefs for x86_64.

* Both filesystems used to link to a static kernel-zlib, which
was being built with -fno-pic. This doesn't work on x86_64 as the
filesystem add-ons are meant to be relocatable, which requires their
code to be compiled as position independent.
Solve that by moving zlib into the kernel, so any add-on can just use
it from there (packagefs is mandatory, so we can't really do without
zlib anyway).

Complete outsourcing of zlib

* Add optional packages Zlib and Zlib-devel.
* Simplify the build feature section for zlib and also extract the
source package.
* Replace all remaining references to the zlib instance in the tree and
remove it.

Switch package kit to BZlibCompressionAlgorithm

... and remove the Zlib{Compressor,Decompressor} API.

2nd attempt at fixing build of btrfs and packagefs.

* adding zlib to the kernel unfortunately introduces a cyclic dependency
with respect to the zlib, haiku and haiku_devel packages (AFAICS)
* circumvent this by building kernel_zlib as a static library again,
this time with PIC, such that it can be used by kernel add-ons

Revert "Fix build problems of btrfs and packagefs for x86_64."

This reverts commit f272e63f393449d3a816970ca632764895a78cd6.

Fix build problems of btrfs and packagefs for x86_64.

* Both filesystems used to link to a static kernel-zlib, which
was being built with -fno-pic. This doesn't work on x86_64 as the
filesystem add-ons are meant to be relocatable, which requires their
code to be compiled as position independent.
Solve that by moving zlib into the kernel, so any add-on can just use
it from there (packagefs is mandatory, so we can't really do without
zlib anyway).

Complete outsourcing of zlib

* Add optional packages Zlib and Zlib-devel.
* Simplify the build feature section for zlib and also extract the
source package.
* Replace all remaining references to the zlib instance in the tree and
remove it.