(#6187) - [libpng] set CMAKE_SYSTEM_PROCESSOR for M1

* - [libpng] set CMAKE_SYSTEM_PROCESSOR for M1

Signed-off-by: SSE4 <tomskside@gmail.com>

* - argh, annoying hook!

recipes/libpng/all/conanfile.py

@@ -26,6 +26,8 @@ def config_options(self):
             del self.options.fPIC
 
     def configure(self):
+        if self.options.shared:
+            del self.options.fPIC
         del self.settings.compiler.libcxx
         del self.settings.compiler.cppstd
 
@@ -70,6 +72,8 @@ def _configure_cmake(self):
                 cmake.definitions["PNG_ARM_NEON"] = "on"
         if self.options.api_prefix:
             cmake.definitions["PNG_PREFIX"] = self.options.api_prefix
+        if self.settings.os == "Macos" and self.settings.arch == "armv8":
+            cmake.definitions["CMAKE_SYSTEM_PROCESSOR"] = "aarch64"
         cmake.configure()
         return cmake