sagemathgh-38522: `build/pkgs/libpng`: Update to 1.6.43
    
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Rebased and updated from sagemath#30564. Fixes sagemath#30564

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### ⌛ Dependencies

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URL: sagemath#38522
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee

Author: Release Manager

build/pkgs/libpng/checksums.ini

@@ -1,3 +1,4 @@
 tarball=libpng-VERSION.tar.gz
-sha1=012c842e6454dc38c6390623ed31ec4005c00584
-sha256=e30bf36cd5882e017c23a5c6a79a9aa1a744dd5841bb45ff7035ec6e3b3096b8
+sha1=eb7ed4d6d4646542fb4b4a0a3f53f7b419cf4965
+sha256=e804e465d4b109b5ad285a8fb71f0dd3f74f0068f91ce3cdfde618180c174925
+upstream_url=https://download.sourceforge.net/libpng/libpng-VERSION.tar.gz

build/pkgs/libpng/package-version.txt

@@ -1 +1 @@
-1.6.29.p1
+1.6.43

build/pkgs/libpng/spkg-install.in

@@ -1,13 +1,8 @@
 # libpng needs to have no default options set for grep
 unset GREP_OPTIONS
 
-export CFLAGS="$CFLAGS -fPIC -g"
-
-# Pick up Sage's zlib:
-export CPPFLAGS="-I$SAGE_LOCAL/include $CPPFLAGS"
-
 cd src
 
-sdh_configure --enable-shared=yes
+sdh_configure --enable-shared --disable-static
 sdh_make
 sdh_make_install