Disable semantic interposition in ELF shared libraries

[Dead2]

Disallow semantic interposition in ELF shared libraries if supported by the compiler.
This disallows calls to our own exported functions being replaced by LD_PRELOAD, thus
avoiding the potential bugs and allowing the compiler to optimize better.

The best/most detailed description of this compiler parameter I have found is here:
https://fedoraproject.org/wiki/Changes/PythonNoSemanticInterpositionSpeedup

I have not been able to reliably measure a performance difference with this, and that is
likely because we rarely call our own exported functions, and never in any hot areas.

This does give a little size reduction for the shared library.

Configure before
   text    data     bss     dec     hex filename
 106832    1368      32  108232   1a6c8 libz-ng.so.1.9.9

Configure with PR
   text    data     bss     dec     hex filename
 106504    1296      32  107832   1a538 libz-ng.so.1.9.9

Cmake before
   text    data     bss     dec     hex filename
 111456    1368      32  112856   1b8d8 libz-ng.so.1.9.9

Cmake with PR
   text    data     bss     dec     hex filename
 111064    1296      32  112392   1b708 libz-ng.so.1.9.9

[codecov]

Codecov Report

Merging #821 (5326715) into develop (446c697) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #821   +/-   ##
========================================
  Coverage    76.67%   76.67%           
========================================
  Files           71       71           
  Lines         7457     7457           
  Branches      1341     1342    +1     
========================================
  Hits          5718     5718           
+ Misses        1211     1210    -1     
- Partials       528      529    +1     

Flag	Coverage Δ
macos_clang	68.60% <ø> (ø)
macos_gcc	67.78% <ø> (ø)
ubuntu_clang	74.93% <ø> (ø)
ubuntu_clang_inflate_allow_invalid_dist	74.85% <ø> (ø)
ubuntu_clang_inflate_strict	75.12% <ø> (ø)
ubuntu_clang_mmap	74.88% <ø> (ø)
ubuntu_clang_msan	74.92% <ø> (ø)
ubuntu_gcc	77.43% <ø> (ø)
ubuntu_gcc_aarch64	76.91% <ø> (ø)
ubuntu_gcc_aarch64_compat_no_opt	74.66% <ø> (ø)
ubuntu_gcc_aarch64_no_acle	75.99% <ø> (ø)
ubuntu_gcc_aarch64_no_neon	75.73% <ø> (ø)
ubuntu_gcc_armhf	77.41% <ø> (ø)
ubuntu_gcc_armhf_compat_no_opt	74.67% <ø> (ø)
ubuntu_gcc_armhf_no_acle	76.42% <ø> (ø)
ubuntu_gcc_armhf_no_neon	76.79% <ø> (ø)
ubuntu_gcc_armsf	77.41% <ø> (ø)
ubuntu_gcc_armsf_compat_no_opt	74.67% <ø> (ø)
ubuntu_gcc_compat_no_opt	75.18% <ø> (ø)
ubuntu_gcc_mingw_x86_64	75.65% <ø> (+0.04%)	⬆️
ubuntu_gcc_no_avx2	76.72% <ø> (ø)
ubuntu_gcc_no_pclmulqdq	75.10% <ø> (ø)
ubuntu_gcc_no_sse2	75.99% <ø> (ø)
ubuntu_gcc_no_sse4	75.11% <ø> (ø)
ubuntu_gcc_o3	75.77% <ø> (ø)
ubuntu_gcc_osb	76.51% <ø> (ø)
ubuntu_gcc_ppc	77.59% <ø> (ø)
ubuntu_gcc_ppc64	76.82% <ø> (ø)
ubuntu_gcc_ppc64le	76.02% <ø> (ø)
ubuntu_gcc_s390x	75.18% <ø> (ø)
ubuntu_gcc_sparc64	78.06% <ø> (+0.96%)	⬆️
win64_gcc	73.11% <ø> (ø)
win64_gcc_compat_no_opt	74.63% <ø> (ø)

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

Impacted Files	Coverage Δ
gzlib.c	54.51% <0.00%> (-0.38%)	⬇️
trees.c	95.79% <0.00%> (-0.33%)	⬇️
inffast.c	90.37% <0.00%> (+1.48%)	⬆️

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[nmoinvaz]

I only had minor questions, otherwise looks good!

[nmoinvaz]

LGTM