Fix aarch64 build.

We recently gained -Werror=missing-prototypes. (See also, we really need to get
those Android bots...)

Change-Id: I3962d3050bccf5f5a057d029b5cbff1695ca1a03
Reviewed-on: https://boringssl-review.googlesource.com/7540
Reviewed-by: Emily Stark (Dunn) <estark@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/crypto/modes/gcm.c b/crypto/modes/gcm.c
index 9255c9d..b857131 100644
--- a/crypto/modes/gcm.c
+++ b/crypto/modes/gcm.c
@@ -392,14 +392,14 @@
 static int neon_capable(void) {
   return 0;
 }
-void gcm_init_neon(u128 Htable[16], const uint64_t Xi[2]) {
+static void gcm_init_neon(u128 Htable[16], const uint64_t Xi[2]) {
   abort();
 }
-void gcm_gmult_neon(uint64_t Xi[2], const u128 Htable[16]) {
+static void gcm_gmult_neon(uint64_t Xi[2], const u128 Htable[16]) {
   abort();
 }
-void gcm_ghash_neon(uint64_t Xi[2], const u128 Htable[16], const uint8_t *inp,
-                    size_t len) {
+static void gcm_ghash_neon(uint64_t Xi[2], const u128 Htable[16],
+                           const uint8_t *inp, size_t len) {
   abort();
 }
 #endif