Added Z_UNUSED define for ignore unused variables.

[nmoinvaz]

Previously mentioned in #418.

I have put it in zbuild.h for now and if we want to it can be moved. I can also rename it to UNUSED() if Z_UNUSED is not good name for zbuild.h.

[mtl1979]

I think the name is acceptable as it follows our naming style. zbuild.h should contain all macros and defines that are supposed to be only used when building zlib-ng library itself or one of the test binaries in same repository. As such any other application or library that links against zlib-ng can define own version even with same name and it shouldn't ever conflict as no externally visible header of zlib-ng should include zbuild.h.

[codecov]

Codecov Report

Merging #997 (340974e) into develop (e2705f8) will not change coverage.
The diff coverage is 84.21%.

@@           Coverage Diff            @@
##           develop     #997   +/-   ##
========================================
  Coverage    76.37%   76.37%           
========================================
  Files           77       77           
  Lines         8250     8250           
  Branches      1342     1339    -3     
========================================
  Hits          6301     6301           
  Misses        1417     1417           
  Partials       532      532           

Flag	Coverage Δ
macos_clang	68.34% <ø> (ø)
macos_gcc	67.21% <ø> (ø)
ubuntu_clang	69.35% <ø> (ø)
ubuntu_clang_debug	68.76% <84.21%> (ø)
ubuntu_clang_inflate_allow_invalid_dist	69.11% <ø> (ø)
ubuntu_clang_inflate_strict	69.35% <ø> (ø)
ubuntu_clang_mmap	69.35% <ø> (ø)
ubuntu_clang_msan	69.35% <ø> (ø)
ubuntu_clang_pigz	35.34% <ø> (ø)
ubuntu_clang_pigz_no_optim	37.79% <ø> (ø)
ubuntu_clang_pigz_no_threads	34.99% <ø> (ø)
ubuntu_gcc	68.53% <ø> (ø)
ubuntu_gcc_aarch64	68.78% <ø> (ø)
ubuntu_gcc_aarch64_compat_no_opt	66.97% <ø> (ø)
ubuntu_gcc_aarch64_no_acle	67.69% <ø> (ø)
ubuntu_gcc_aarch64_no_neon	67.98% <ø> (ø)
ubuntu_gcc_armhf	68.75% <ø> (ø)
ubuntu_gcc_armhf_compat_no_opt	66.94% <ø> (ø)
ubuntu_gcc_armhf_no_acle	68.91% <ø> (ø)
ubuntu_gcc_armhf_no_neon	69.15% <ø> (ø)
ubuntu_gcc_armsf	68.76% <ø> (ø)
ubuntu_gcc_armsf_compat_no_opt	66.94% <ø> (ø)
ubuntu_gcc_compat_no_opt	68.42% <ø> (ø)
ubuntu_gcc_mingw_i686	0.00% <ø> (ø)
ubuntu_gcc_mingw_x86_64	0.00% <ø> (ø)
ubuntu_gcc_no_avx2	68.76% <ø> (ø)
ubuntu_gcc_no_pclmulqdq	66.71% <ø> (ø)
ubuntu_gcc_no_sse2	67.94% <ø> (ø)
ubuntu_gcc_no_sse4	66.89% <ø> (ø)
ubuntu_gcc_o3	68.31% <ø> (ø)
ubuntu_gcc_osb	70.86% <88.88%> (ø)
ubuntu_gcc_pigz	35.30% <ø> (+0.05%)	⬆️
ubuntu_gcc_ppc	68.91% <ø> (ø)
ubuntu_gcc_ppc64	69.78% <ø> (ø)
ubuntu_gcc_ppc64le	68.47% <ø> (ø)
ubuntu_gcc_s390x	67.79% <ø> (ø)
ubuntu_gcc_sparc64	70.07% <ø> (ø)
win64_gcc	70.16% <ø> (ø)
win64_gcc_compat_no_opt	73.57% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
deflate.h	33.33% <ø> (ø)
trees_emit.h	82.55% <0.00%> (ø)
zutil.c	35.71% <0.00%> (ø)
inflate.c	87.55% <100.00%> (ø)
test/example.c	77.15% <100.00%> (ø)
test/fuzz/checksum_fuzzer.c	94.23% <100.00%> (ø)
test/fuzz/standalone_fuzz_target_runner.c	100.00% <100.00%> (ø)
test/infcover.c	90.69% <100.00%> (ø)

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[Dead2]

LGTM