gh-40460: move zlib to prereqs, remove zlib spkg
    
move zlib to prereqs, remove zlib spkg. Provide macos-specific zlib.pc
which is used to point at the system zlib,
which is always there.

### 📝 Checklist

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- [ ] The title is concise and informative.
- [ ] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

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<!-- - #12345: short description why this is a dependency -->
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URL: #40460
Reported by: Dima Pasechnik
Reviewer(s): Tobias Diez

Author: Release Manager

COPYING.txt

@@ -69,7 +69,7 @@ jmol                        LGPLv2.1+
 jsonschema                  MIT License
 lcalc                       GPLv2+
 libgap                      GPLv3+
-libpng                      Custom, very similar to zlib
+libpng                      Custom (modified BSD)
 linbox                      LGPLv2.1+
 lrcalc                      GPLv2+
 m4ri                        GPLv2+
@@ -124,7 +124,6 @@ sympy                       Modified BSD
 tachyon                     Modified BSD
 threejs                     MIT License
 tornado                     Apache License
-zlib                        Custom (Modified BSD)
 
 CONTACT INFO:
      William Stein; [email protected];
@@ -1314,30 +1313,3 @@ modification, are permitted provided that the following conditions are met:
 [followed by the BSD disclaimer]
 
 ================================================================================
-
-zlib:
-GPL compatible according to
-  http://www.fsf.org/licensing/licenses/index_html#GPLCompatibleLicenses
-
-Copyright (C) 1995-2004 Jean-loup Gailly and Mark Adler
-
-  This software is provided 'as-is', without any express or implied
-  warranty.  In no event will the authors be held liable for any damages
-  arising from the use of this software.
-
-  Permission is granted to anyone to use this software for any purpose,
-  including commercial applications, and to alter it and redistribute it
-  freely, subject to the following restrictions:
-
-  1. The origin of this software must not be misrepresented; you must not
-     claim that you wrote the original software. If you use this software
-     in a product, an acknowledgment in the product documentation would be
-     appreciated but is not required.
-  2. Altered source versions must be plainly marked as such, and must not be
-     misrepresented as being the original software.
-  3. This notice may not be removed or altered from any source distribution.
-
-  Jean-loup Gailly [email protected]
-  Mark Adler [email protected]
-
-===============================================================================

README.md

@@ -17,7 +17,6 @@
 #   4ti2
 #   autotools
 #   [...]
-#   zlib
 #
 # * Find the package name given a tarball filename
 #

build/bin/sage-package

@@ -313,7 +313,7 @@ toolchain: $(foreach pkgname,$(TOOLCHAIN),$(inst_$(pkgname))) $(PCFILES)
 # See #14168 and #14232.
 #
 # Note: This list consists of only the *runtime* dependencies of the toolchain.
-TOOLCHAIN_DEPS = zlib $(MP_LIBRARY) mpfr mpc
+TOOLCHAIN_DEPS = $(MP_LIBRARY) mpfr mpc
 TOOLCHAIN_DEP_INSTS = \
 	$(foreach pkgname,$(TOOLCHAIN_DEPS),$(inst_$(pkgname)))
 
@@ -569,7 +569,7 @@ pkg_deps = \
 #
 # For example, for python3 this will expand to:
 #
-# $(INST)/python3-3.7.3: $(inst_zlib) $(inst_readline) $(inst_sqlite) $(inst_libpng) $(inst_xz) $(inst_libffi)
+# $(INST)/python3-3.7.3: $(inst_readline) $(inst_sqlite) $(inst_libpng) $(inst_xz) $(inst_libffi)
 #     +$(AM_V_at)sage-logger -p '$(SAGE_SPKG) python3-3.7.3' '$(SAGE_LOGS)/python3-3.7.3.log'
 #
 # python3: $(INST)/python3-3.7.3

build/make/Makefile.in

@@ -1,4 +1,4 @@
-zlib $(MP_LIBRARY) glpk
+$(MP_LIBRARY) glpk
 
 ----------
 All lines of this file are ignored except the first.

build/pkgs/4ti2/dependencies

@@ -1,5 +1,5 @@
 SAGE_SPKG_CONFIGURE([4ti2], [
-    SAGE_SPKG_DEPCHECK([gmp glpk zlib], [
+    SAGE_SPKG_DEPCHECK([gmp glpk], [
         dnl Debian installs these programs with an executable prefix "4ti2-",
         dnl OpenSUSE uses the prefix "4ti2_".
         dnl Singular checks for unprefixed and prefixed with "4ti2-".

build/pkgs/4ti2/spkg-configure.m4

@@ -22,3 +22,4 @@ patch
 bzip2
 patch
 pkgconf
+zlib-dev

build/pkgs/_prereq/SPKG.rst

@@ -20,3 +20,4 @@ bzip2
 which
 patch
 pkgconf
+zlib

build/pkgs/_prereq/distros/alpine.txt

@@ -17,3 +17,5 @@ bc
 patch
 bzip2
 pkg-config
+zlib
+zlib-devel