Fix fiat asm .private_extern declaration on Apple platforms

Chromium actually has a checker for unexpected exported symbols, which
caught this.

Change-Id: If1af4c26a3326eea185725f9e84c17f5d9f0f58e
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/60665
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
Auto-Submit: David Benjamin <davidben@google.com>
diff --git a/third_party/fiat/asm/fiat_curve25519_adx_mul.S b/third_party/fiat/asm/fiat_curve25519_adx_mul.S
index f91e67d..28b1745 100644
--- a/third_party/fiat/asm/fiat_curve25519_adx_mul.S
+++ b/third_party/fiat/asm/fiat_curve25519_adx_mul.S
@@ -8,7 +8,7 @@
 .intel_syntax noprefix
 .text
 #if defined(__APPLE__)
-.private_extern fiat_curve25519_adx_mul
+.private_extern _fiat_curve25519_adx_mul
 .global _fiat_curve25519_adx_mul
 _fiat_curve25519_adx_mul:
 #else
diff --git a/third_party/fiat/asm/fiat_curve25519_adx_square.S b/third_party/fiat/asm/fiat_curve25519_adx_square.S
index 027dcf1..8881821 100644
--- a/third_party/fiat/asm/fiat_curve25519_adx_square.S
+++ b/third_party/fiat/asm/fiat_curve25519_adx_square.S
@@ -8,7 +8,7 @@
 .intel_syntax noprefix
 .text
 #if defined(__APPLE__)
-.private_extern fiat_curve25519_adx_square
+.private_extern _fiat_curve25519_adx_square
 .global _fiat_curve25519_adx_square
 _fiat_curve25519_adx_square:
 #else