Fix build on aarch64.

from Brad (maintainer)

multimedia/aom/patches/patch-build_cmake_aom_configure_cmake

@@ -0,0 +1,25 @@
+$OpenBSD: patch-build_cmake_aom_configure_cmake,v 1.5 2020/03/15 11:10:36 ajacoutot Exp $
+
+ARM uses compiler intrinsics, so don't require GNU as.
+
+Index: build/cmake/aom_configure.cmake
+--- build/cmake/aom_configure.cmake.orig
++++ build/cmake/aom_configure.cmake
+@@ -162,17 +162,6 @@ elseif("${AOM_TARGET_CPU}" MATCHES "arm")
+       set(AS_EXECUTABLE as)
+     endif()
+   endif()
+-  find_program(as_executable_found ${AS_EXECUTABLE})
+-  if(NOT as_executable_found)
+-    message(
+-      FATAL_ERROR
+-        "Unable to find assembler and optimizations are enabled."
+-        "Searched for ${AS_EXECUTABLE}. Install it, add it to your path, or "
+-        "set the assembler directly by adding -DAS_EXECUTABLE=<assembler path> "
+-        "to your CMake command line."
+-        "To build without optimizations, add -DAOM_TARGET_CPU=generic to your "
+-        "cmake command line.")
+-  endif()
+   string(STRIP "${AOM_AS_FLAGS}" AOM_AS_FLAGS)
+ endif()
+