externals: Amend zlib submodule

Supplies CMakeLists.txt file that avoids pulling in zlib's tests into
the tree. This avoids needing to explicitly opt these tests out from
ctest.

.ci/scripts/linux/docker.sh

@@ -11,5 +11,4 @@ ninja
 
 ccache -s
 
-# Ignore zlib's tests, since they aren't gated behind a CMake option.
-ctest -VV -E "(example|example64)" -C Release
+ctest -VV -C Release

.gitmodules

@@ -50,5 +50,5 @@
     path = externals/libzip
     url = https://github.com/DarkLordZach/libzip
 [submodule "zlib"]
-    path = externals/zlib
-    url = https://github.com/madler/zlib
+	path = externals/zlib/zlib
+	url = https://github.com/madler/zlib.git

externals/zlib/CMakeLists.txt

@@ -0,0 +1,81 @@
+project(zlib C)
+
+include(CheckTypeSize)
+include(CheckFunctionExists)
+include(CheckIncludeFile)
+
+check_include_file(sys/types.h HAVE_SYS_TYPES_H)
+check_include_file(stdint.h    HAVE_STDINT_H)
+check_include_file(stddef.h    HAVE_STDDEF_H)
+
+# Check to see if we have large file support
+set(CMAKE_REQUIRED_DEFINITIONS -D_LARGEFILE64_SOURCE=1)
+# We add these other definitions here because CheckTypeSize.cmake
+# in CMake 2.4.x does not automatically do so and we want
+# compatibility with CMake 2.4.x.
+if(HAVE_SYS_TYPES_H)
+    list(APPEND CMAKE_REQUIRED_DEFINITIONS -DHAVE_SYS_TYPES_H)
+endif()
+if(HAVE_STDINT_H)
+    list(APPEND CMAKE_REQUIRED_DEFINITIONS -DHAVE_STDINT_H)
+endif()
+if(HAVE_STDDEF_H)
+    list(APPEND CMAKE_REQUIRED_DEFINITIONS -DHAVE_STDDEF_H)
+endif()
+check_type_size(off64_t OFF64_T)
+if(HAVE_OFF64_T)
+   add_definitions(-D_LARGEFILE64_SOURCE=1)
+endif()
+set(CMAKE_REQUIRED_DEFINITIONS) # clear variable
+
+# Check for fseeko
+check_function_exists(fseeko HAVE_FSEEKO)
+if(NOT HAVE_FSEEKO)
+    add_definitions(-DNO_FSEEKO)
+endif()
+
+# Check for unistd.h
+check_include_file(unistd.h HAVE_UNISTD_H)
+if(HAVE_UNISTD_H)
+    add_definitions(-DHAVE_UNISTD_H)
+endif()
+
+if(MSVC)
+    add_definitions(-D_CRT_SECURE_NO_DEPRECATE)
+    add_definitions(-D_CRT_NONSTDC_NO_DEPRECATE)
+endif()
+
+add_library(z STATIC
+    zlib/adler32.c
+    zlib/compress.c
+    zlib/crc32.c
+    zlib/crc32.h
+    zlib/deflate.c
+    zlib/deflate.h
+    zlib/gzclose.c
+    zlib/gzguts.h
+    zlib/gzlib.c
+    zlib/gzread.c
+    zlib/gzwrite.c
+    zlib/inffast.h
+    zlib/inffixed.h
+    zlib/inflate.c
+    zlib/inflate.h
+    zlib/infback.c
+    zlib/inftrees.c
+    zlib/inftrees.h
+    zlib/inffast.c
+    zlib/trees.c
+    zlib/trees.h
+    zlib/uncompr.c
+    zlib/zconf.h
+    zlib/zlib.h
+    zlib/zutil.c
+    zlib/zutil.h
+)
+add_library(ZLIB::ZLIB ALIAS z)
+
+target_include_directories(z
+PUBLIC
+    zlib/
+)