Also automatically detect macOS version and SDK

Author: giordano

base/loading.jl

@@ -1784,9 +1784,13 @@ function ld()
     elseif Sys.isapple()
         flavor = "darwin"
         arch = Sys.ARCH == :aarch64 ? :arm64 : Sys.ARCH
-        # TODO: gently handle failure in `xcrun` (command not found, garbage being returned, etc...)
+        # TODO: gently handle failure in `xcrun`/`sw_vers` (command not found, garbage being
+        # returned, etc...).  We probably also want to provide ways to override platform
+        # version and SDK, for when we build the release binaries.
         sysroot = readchomp(`xcrun --sdk macosx --show-sdk-path`)
-        default_args = `-arch $arch -syslibroot $(sysroot) -lSystem -platform_version macos 10 11`
+        platform_version = readchomp(`sw_vers -productVersion`)
+        platform_sdk = readchomp(`xcrun --show-sdk-version`)
+        default_args = `-arch $arch -syslibroot $(sysroot) -lSystem -platform_version macos $(platform_version) $(platform_sdk)`
     else
         flavor = "gnu"
     end