reverting change to compatibility_version

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@141445 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/buildit b/lib/buildit
index d6e6afc..d78bd3d 100755
--- a/lib/buildit
+++ b/lib/buildit
@@ -71,7 +71,7 @@
 	    LDSHARED_FLAGS="-o libc++.1.dylib \
 			-dynamiclib -nodefaultlibs  \
 			-current_version ${RC_ProjectSourceVersion} \
-			-compatibility_version ${RC_ProjectSourceVersion} \
+			-compatibility_version 1 \
 			-install_name /usr/lib/libc++.1.dylib \
 			-lSystem  \
 			-Wl,-unexported_symbols_list,libc++unexp.exp  \