Fix cross/zlib

[hgy59]

Description

This is an extract of #5414 where it fixed the usage of OpenEXR format, rsvg-convert (at runtime) and gdk-pixbuf.

• the generated zlib.pc had wrong prefix
• this caused problems in dependent libraries and binaries

Checklist

• Build rule all-supported completed successfully
• New installation of package completed successfully
• Package upgrade completed successfully (Manually install the package again)
• Package functionality was tested
• Any needed documentation is updated/created

Type of change

• Bug fix

[hgy59]

@th0ma7 did you ever face problems with zlib?

This fix is probably mandatory for ffmpeg too (while you are working on it...)

[th0ma7]

I never faced (or noticed) this... and ffmpeg clearly is a candidate for it due to its amount of dependencies. Nice catch.

[hgy59]

Without this fix, shared libraries (or binaries) had a flase reference to zlib like:
(example from cross/openexr)

Dynamic section at offset 0x2c6c98 contains 36 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [libImath-2_5.so.25]
 0x0000000000000001 (NEEDED)             Shared library: [libIlmThread-2_5.so.25]
 0x0000000000000001 (NEEDED)             Shared library: [/spksrc/spk/imagemagick/work-aarch64-6.1/install/var/packages/imagemagick/target/lib/libz.so]
 0x0000000000000001 (NEEDED)             Shared library: [libHalf-2_5.so.25]
 0x0000000000000001 (NEEDED)             Shared library: [libIexMath-2_5.so.25]
 0x0000000000000001 (NEEDED)             Shared library: [libIex-2_5.so.25]
 0x0000000000000001 (NEEDED)             Shared library: [libstdc++.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libm.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libgcc_s.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libpthread.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x000000000000000e (SONAME)             Library soname: [libIlmImf-2_5.so.26]
 0x000000000000001d (RUNPATH)            Library runpath: [/var/packages/imagemagick/target/lib]

[th0ma7]

Long shot but wonder if that could be the cause of deluge segfault... will rebase and test, just in case.