libvpx: fix configuration for arm64

* Disable switch to the iphoneos sdk for arm targets
* Disable unsupported "runtime-cpu-detect" feature on arm64
* Add arm64 to `supported_archs`

Fixes: https://trac.macports.org/ticket/60940

multimedia/libvpx/Portfile

@@ -32,7 +32,7 @@ git.url             https://chromium.googlesource.com/webm/${name}
 git.branch          v${version}
 
 # support for non-intel archs removed in version 1.5.0
-supported_archs     x86_64 i386
+supported_archs     x86_64 i386 arm64
 
 depends_build-append port:yasm
 
@@ -72,6 +72,14 @@ configure.args      --enable-vp8 \
                     --disable-examples \
                     --disable-unit-tests
 
+# libvpx does not yet support runtime detection of NEON features on macOS/iOS.
+# For arm64 builds (and universal builds targeting arm) we disable this feature,
+# meaning NEON support is determined at compile time.
+# For x86* architectures in universal builds, this feature is re-enabled below.
+if { ${build_arch} eq "arm64" || [variant_isset universal] } {
+    configure.args-delete --enable-runtime-cpu-detect
+}
+
 configure.env       LD=${configure.cc}
 
 # add in when docs are installed correctly
@@ -113,6 +121,7 @@ foreach my_arch {i386 x86_64} {
     if {[info exists my_targets(${my_arch})]} {
         set merger_configure_args(${my_arch}) --force-target=$my_targets(${my_arch})-${os.platform}-gcc
     }
+    lappend merger_configure_args(${my_arch}) --enable-runtime-cpu-detect
 }
 if {![info exists universal_possible]} {
     set universal_possible [expr {${os.universal_supported} && [llength ${configure.universal_archs}] >= 2}]

multimedia/libvpx/files/patch-build-make-configure.sh.diff

@@ -1,11 +1,30 @@
---- build/make/configure.sh.orig	2020-08-01 00:27:21.000000000 +0200
-+++ build/make/configure.sh	2020-08-01 00:29:56.000000000 +0200
-@@ -854,7 +854,7 @@
-       fi
-       ;;
-     x86*-darwin*)
+--- build/make/configure.sh.orig	2020-11-26 14:23:30.000000000 -0800
++++ build/make/configure.sh	2020-11-26 14:26:37.000000000 -0800
+@@ -845,16 +845,8 @@
+   # Handle darwin variants. Newer SDKs allow targeting older
+   # platforms, so use the newest one available.
+   case ${toolchain} in
+-    arm*-darwin*)
+-      add_cflags "-miphoneos-version-min=${IOS_VERSION_MIN}"
+-      iphoneos_sdk_dir="$(show_darwin_sdk_path iphoneos)"
+-      if [ -d "${iphoneos_sdk_dir}" ]; then
+-        add_cflags  "-isysroot ${iphoneos_sdk_dir}"
+-        add_ldflags "-isysroot ${iphoneos_sdk_dir}"
+-      fi
+-      ;;
+-    x86*-darwin*)
 -      osx_sdk_dir="$(show_darwin_sdk_path macosx)"
++    *-darwin*)
 +      osx_sdk_dir="$(configure.sdkroot)"
        if [ -d "${osx_sdk_dir}" ]; then
          add_cflags  "-isysroot ${osx_sdk_dir}"
          add_ldflags "-isysroot ${osx_sdk_dir}"
+@@ -1085,7 +1077,7 @@
+           ;;
+
+         darwin*)
+-          if ! enabled external_build; then
++          if false; then
+             XCRUN_FIND="xcrun --sdk iphoneos --find"
+             CXX="$(${XCRUN_FIND} clang++)"
+             CC="$(${XCRUN_FIND} clang)"