Remove string.h from base.h.
Including string.h in base.h causes any file that includes a BoringSSL
header to include string.h. Generally this wouldn't be a problem,
although string.h might slow down the compile if it wasn't otherwise
needed. However, it also causes problems for ipsec-tools in Android
because OpenSSL didn't have this behaviour.
This change removes string.h from base.h and, instead, adds it to each
.c file that requires it.
Reviewed-by: David Benjamin <email@example.com>
Reviewed-by: Adam Langley <firstname.lastname@example.org>
diff --git a/crypto/hkdf/hkdf.c b/crypto/hkdf/hkdf.c
index be51bc3..bb7f5a4 100644
@@ -15,6 +15,7 @@