osx: add a way to compile for older versions of OS X

diff --git a/README.md b/README.md
index 8cd59a12ac1cee56d8318157bd32559bc5cc2edb..cff762161818e50f7d4e242321efacb6c2d338c8 100644 (file)
--- a/README.md
+++ b/README.md
@@ -84,10 +84,20 @@ simpler alternatives:
     version of OS X (it is important to use a separate build
     directory):
  
-        mkdir build
+        mkdir build && cd build
         ../configure --prefix=/usr --sysconfdir=/etc --with-embedded-libevent
         make -C osx pkg ARCHS="i386 x86_64"
 
+    If you want to compile for an older version of Mac OS X, you need
+    to find the right SDK and issues commands like those:
+
+        SDK=/Developer/SDKs/MacOSX10.6.sdk
+        mkdir build && cd build
+        ../configure --prefix=/usr --sysconfdir=/etc --with-embedded-libevent \
+           CFLAGS="-mmacosx-version-min=10.6 -isysroot $SDK" \
+           LDFLAGS="-mmacosx-version-min=10.6 -isysroot $SDK"
+        make -C osx pkg ARCHS="i386 x86_64"
+
 If you don't follow the above procedures, you will have to create the
 user/group `_lldpd`. Have a look at how this is done in
 `osx/scripts/postinstall`.