Check memory is zeroized

Add a define WOLFSSL_CHECK_MEM_ZERO to turn on code that checks that
memory that must be zeroized before going out of use is zero.
Everytime sensitive data is put into a allocated buffer or stack buffer;
the address, its length and a name is stored to be checked later.
Where the stack buffer is about to go out of use, a call is added to
check that the required parts are zero.

wc_MemZero_Add() adds an address with length and name to a table of
addressed to be checked later.
wc_MemZero_Check() checks that the memory associated with the address is
zeroized where required.
mp_memzero_add() adds mp_int's data pointer with length and name to
table.
mp_memzero_check() checks that the data pointer is zeroized where
required.

Freeing memory will check the address. The length was prepended on
allocation.
Realloction was changed for WOLFSSL_CHECK_MEM_ZERO to perform an
allocate, check, copy, free.

tests/api.c

@@ -19107,6 +19107,10 @@ static int test_wc_RsaKeyToDer (void)
                 /* Try Public Key. */
                 genKey.type = 0;
                 ret = wc_RsaKeyToDer(&genKey, der, FOURK_BUF);
+            #ifdef WOLFSSL_CHECK_MEM_ZERO
+                /* Put back to Private Key */
+                genKey.type = 1;
+            #endif
             }
             if (ret == BAD_FUNC_ARG) {
                 ret = 0;
@@ -19126,6 +19130,10 @@ static int test_wc_RsaKeyToDer (void)
                 /* Try Public Key. */
                 genKey.type = 0;
                 ret = wc_RsaKeyToDer(&genKey, der, FOURK_BUF);
+            #ifdef WOLFSSL_CHECK_MEM_ZERO
+                /* Put back to Private Key */
+                genKey.type = 1;
+            #endif
             }
             if (ret == USER_CRYPTO_ERROR) {
                 ret = 0;