Expose two, rather internal, BIGNUM functions.

Android uses these for some conversions from Java formats. The code is
sufficiently bespoke that putting the conversion functions into
BoringSSL doesn't make a lot of sense, but the alternative is to expose
these ones.

Change-Id: If1362bc4a5c44cba4023c909e2ba6488ae019ddb

crypto/bn/internal.h

@@ -131,19 +131,10 @@
 extern "C" {
 #endif
 
-/* BN_wexpand ensures that |bn| has at least |words| works of space without
- * altering its value. It returns one on success or zero on allocation
- * failure. */
-BIGNUM *bn_wexpand(BIGNUM *bn, unsigned words);
-
 /* bn_expand acts the same as |BN_wexpand|, but takes a number of bits rather
  * than a number of words. */
 BIGNUM *bn_expand(BIGNUM *bn, unsigned bits);
 
-/* bn_correct_top decrements |bn->top| until |bn->d[top-1]| is non-zero or
- * until |top| is zero. */
-void bn_correct_top(BIGNUM *bn);
-
 #if defined(OPENSSL_64_BIT)
 
 #define BN_ULLONG	unsigned long long

include/openssl/bn.h

@@ -284,6 +284,22 @@ OPENSSL_EXPORT int BN_print_fp(FILE *fp, const BIGNUM *a);
 OPENSSL_EXPORT BN_ULONG BN_get_word(const BIGNUM *bn);
 
 
+/* Internal functions.
+ *
+ * These functions are useful for code that is doing low-level manipulations of
+ * BIGNUM values. However, be sure that no other function in this file does
+ * what you want before turning to these. */
+
+/* bn_correct_top decrements |bn->top| until |bn->d[top-1]| is non-zero or
+ * until |top| is zero. */
+OPENSSL_EXPORT void bn_correct_top(BIGNUM *bn);
+
+/* bn_wexpand ensures that |bn| has at least |words| works of space without
+ * altering its value. It returns one on success or zero on allocation
+ * failure. */
+OPENSSL_EXPORT BIGNUM *bn_wexpand(BIGNUM *bn, unsigned words);
+
+
 /* BIGNUM pools.
  *
  * Certain BIGNUM operations need to use many temporary variables and