external/boringssl: Sync to 8ebeabf0e2e01b331e56d0a491c12539baa55d3d.

This includes the following changes:

https://boringssl.googlesource.com/boringssl/+log/be2ee342d3781ddb954f91f8a7e660c6f59e87e5..8ebeabf0e2e01b331e56d0a491c12539baa55d3d

Test: Libcore CTS presubmits.
Change-Id: I2fefc3e2bc2bbc3e3083668bd2a56d491520bc24
diff --git a/src/crypto/bn/sqrt.c b/src/crypto/bn/sqrt.c
index fb962a9..f806ea2 100644
--- a/src/crypto/bn/sqrt.c
+++ b/src/crypto/bn/sqrt.c
@@ -148,7 +148,7 @@
     }
     q->neg = 0;
     if (!BN_add_word(q, 1) ||
-        !BN_mod_exp(ret, A, q, p, ctx)) {
+        !BN_mod_exp_mont(ret, A, q, p, ctx, NULL)) {
       goto end;
     }
     err = 0;
@@ -193,7 +193,7 @@
       goto end;
     }
     q->neg = 0;
-    if (!BN_mod_exp(b, t, q, p, ctx)) {
+    if (!BN_mod_exp_mont(b, t, q, p, ctx, NULL)) {
       goto end;
     }
 
@@ -281,7 +281,7 @@
 
   /* Now that we have some non-square, we can find an element
    * of order  2^e  by computing its q'th power. */
-  if (!BN_mod_exp(y, y, q, p, ctx)) {
+  if (!BN_mod_exp_mont(y, y, q, p, ctx, NULL)) {
     goto end;
   }
   if (BN_is_one(y)) {
@@ -327,7 +327,7 @@
       goto end;
     }
   } else {
-    if (!BN_mod_exp(x, A, t, p, ctx)) {
+    if (!BN_mod_exp_mont(x, A, t, p, ctx, NULL)) {
       goto end;
     }
     if (BN_is_zero(x)) {