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

build-llvm.sh

@@ -241,8 +241,27 @@ if [ -n "$LTO" ]; then
 fi
 
 if [ -n "$MACOS_REDIST" ]; then
-    CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_OSX_ARCHITECTURES=arm64;x86_64"
-    CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_OSX_DEPLOYMENT_TARGET=10.9"
+    : ${MACOS_REDIST_ARCHS:=arm64 x86_64}
+    : ${MACOS_REDIST_VERSION:=10.9}
+    ARCH_LIST=""
+    NATIVE=
+    for arch in $MACOS_REDIST_ARCHS; do
+        if [ -n "$ARCH_LIST" ]; then
+            ARCH_LIST="$ARCH_LIST;"
+        fi
+        ARCH_LIST="$ARCH_LIST$arch"
+        if [ "$(uname -m)" = "$arch" ]; then
+            NATIVE=1
+        fi
+    done
+    CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_OSX_ARCHITECTURES=$ARCH_LIST"
+    CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_OSX_DEPLOYMENT_TARGET=$MACOS_REDIST_VERSION"
+    if [ -z "$NATIVE" ]; then
+        # If we're not building for the native arch, flag to CMake that we're
+        # cross compiling, to let it build native versions of tools used
+        # during the build.
+        CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_SYSTEM_NAME=Darwin"
+    fi
 fi
 
 if [ -z "$HOST" ] && [ "$(uname)" = "Darwin" ]; then