Change default iOS dev path

This can be manually overridden with --libc=

Change-Id: I0b857c751d5dc5423f79785e934bc8a714758e75
diff --git a/build/make/configure.sh b/build/make/configure.sh
index 4d0cad2..23dc87f 100755
--- a/build/make/configure.sh
+++ b/build/make/configure.sh
@@ -918,7 +918,7 @@
             add_ldflags -arch_only ${tgt_isa}
 
             if [ -z "${alt_libc}" ]; then
-                alt_libc=${SDK_PATH}/SDKs/iPhoneOS5.1.sdk
+                alt_libc=${SDK_PATH}/SDKs/iPhoneOS6.0.sdk
             fi
 
             add_cflags  "-isysroot ${alt_libc}"