Allow |CRYPTO_is_NEON_capable| to be known at compile time, if possible.

If -mfpu=neon is passed then we don't need to worry about checking for
NEON support at run time. This change allows |CRYPTO_is_NEON_capable| to
statically return 1 in this case. This then allows the compiler to
discard generic code in several cases.

Change-Id: I3b229740ea3d5cb0a304f365c400a0996d0c66ef
Reviewed-on: https://boringssl-review.googlesource.com/6523
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

crypto/cpu-arm.c

diff --git a/crypto/cpu-arm.c b/crypto/cpu-arm.c
index 14ad2ee..675d174 100644
--- a/crypto/cpu-arm.c
+++ b/crypto/cpu-arm.c
@@ -34,7 +34,7 @@
 
 extern uint32_t OPENSSL_armcap_P;
 
-char CRYPTO_is_NEON_capable(void) {
+char CRYPTO_is_NEON_capable_at_runtime(void) {
   return (OPENSSL_armcap_P & ARMV7_NEON) != 0;
 }