- Honor CFLAGS and DEBUG
- Use system libpng on arm platforms

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -1080,16 +1080,6 @@ add_library(cityhash STATIC
 )
 target_include_directories(cityhash PRIVATE ext/cityhash)
 
-if(NOT MSVC)
-	# These can be fast even for debug.
-	target_compile_options(udis86 PRIVATE "-O2")
-	target_compile_options(cityhash PRIVATE "-O2")
-	if(NOT ZLIB_FOUND)
-		target_compile_options(zlib PRIVATE "-O2")
-	endif()
-endif()
-
-
 find_package(LIBZIP)
 if(LIBZIP_FOUND AND USE_SYSTEM_LIBZIP)
 	include_directories(${LIBZIP_INCLUDE_DIRS})
@@ -1233,7 +1223,7 @@ else()
 endif()
 
 # Arm platforms require at least libpng17.
-if(ANDROID OR ARMV7 OR ARM64 OR ARM OR IOS)
+if(ANDROID OR IOS)
 	set(PNG_REQUIRED_VERSION 1.7)
 else()
 	set(PNG_REQUIRED_VERSION 1.6)
