Add gdb script to test mbedtls_zeroize()

The gdb script loads the programs/test/zeroize program and feeds it as
imput its own source code. Then sets a breakpoint just before the last
program's return code and checks that every element in memory was
zeroized. Otherwise it signals a failure and terminates.

The test was added to all.sh.

tests/scripts/all.sh

@@ -421,7 +421,7 @@ export GNUTLS_SERV="$GNUTLS_SERV"
 # Make sure the tools we need are available.
 check_tools "$OPENSSL" "$OPENSSL_LEGACY" "$GNUTLS_CLI" "$GNUTLS_SERV" \
             "$GNUTLS_LEGACY_CLI" "$GNUTLS_LEGACY_SERV" "doxygen" "dot" \
-            "arm-none-eabi-gcc" "i686-w64-mingw32-gcc"
+            "arm-none-eabi-gcc" "i686-w64-mingw32-gcc" "gdb"
 if [ $RUN_ARMCC -ne 0 ]; then
     check_tools "$ARMC5_CC" "$ARMC5_AR" "$ARMC6_CC" "$ARMC6_AR"
 fi

tests/scripts/test_zeroize.gdb

@@ -0,0 +1,25 @@
+set confirm off
+file ./programs/test/zeroize
+break zeroize.c:90
+
+set args ./programs/test/zeroize.c
+run
+
+set $i = 0
+set $len = sizeof(buf)
+set $buf = buf
+
+if exit_code != 0
+    echo The program did not terminate correctly\n
+    quit 1
+end
+
+while $i < $len
+    if $buf[$i++] != 0
+        echo The buffer at was not zeroized\n
+        quit 1
+    end
+end
+
+echo The buffer was correctly zeroized\n
+quit 0