Set macOS deployment target to macOS 10.4
Without a macOS deployment target, the resulting library does not work on macOS versions lower than it was currently built on.
For example, if libslirp was built on macOS 10.15, it would not work on macOS 10.14.
diff --git a/meson.build b/meson.build
index 12c12e7..82bc074 100644
--- a/meson.build
+++ b/meson.build
@@ -113,6 +113,11 @@
   vflag += vflag_test
 endif
 
+if host_system == 'darwin'
+  cargs += '-mmacosx-version-min=10.4'
+  vflag += '-mmacosx-version-min=10.4'
+endif
+
 install_devel = not meson.is_subproject()
 
 configure_file(