Allow cmake 'out-of-source' builds

Allow mbed TLS to be build in a subdirectory. Also add a test in
all.sh
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 9ef4fb9..27a71f6 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -42,7 +42,7 @@
 : ${GNUTLS_LEGACY_SERV:="$GNUTLS_SERV"}
 : ${OUT_OF_SOURCE_DIR:=./mbedtls_out_of_source_build}
 
-usage()
+sage()
 {
     printf "Usage: $0\n"
     printf "  -h|--help\t\tPrint this help.\n"