Allow overriding what archs to build for, or what version to target, for MACOS_REDIST builds

build-mingw-w64-tools.sh

@@ -74,9 +74,26 @@ else
 fi
 if [ -n "$MACOS_REDIST" ]; then
     if [ -z "$CFLAGS" ]; then
-        export CFLAGS="-g -O2"
+        CFLAGS="-g -O2"
     fi
-    export CFLAGS="$CFLAGS -arch arm64 -arch x86_64 -mmacosx-version-min=10.9"
+    : ${MACOS_REDIST_ARCHS:=arm64 x86_64}
+    : ${MACOS_REDIST_VERSION:=10.9}
+    NONNATIVE_ARCH=
+    for arch in $MACOS_REDIST_ARCHS; do
+        CFLAGS="$CFLAGS -arch $arch"
+        if [ "$(uname -m)" != "$arch" ]; then
+            case $arch in
+            arm64) NONNATIVE_ARCH=aarch64 ;;
+            *)     NONNATIVE_ARCH=$arch ;;
+            esac
+        fi
+    done
+    if [ -n "$NONNATIVE_ARCH" ]; then
+        # If we're not building for the native arch, flag that we're
+        # cross compiling.
+        CONFIGFLAGS="$CONFIGFLAGS --host=$NONNATIVE_ARCH-apple-darwin"
+    fi
+    export CFLAGS="$CFLAGS -mmacosx-version-min=$MACOS_REDIST_VERSION"
 fi
 if [ -n "$SKIP_INCLUDE_TRIPLET_PREFIX" ]; then
     INCLUDEDIR="$PREFIX/include"