Merge pull request #36 from wolfSSL/rsa-sha-fix

Link sha256.o module even if sha3 is selected, as it's needed by RSA

arch.mk

@@ -13,9 +13,9 @@ ARCH_FLASH_OFFSET=0x0
 # Default SPI driver name
 SPI_TARGET=$(TARGET)
 
+
 ## Hash settings
 ifeq ($(HASH),SHA256)
-  WOLFCRYPT_OBJS+=./lib/wolfssl/wolfcrypt/src/sha256.o
   CFLAGS+=-DWOLFBOOT_HASH_SHA256
 endif
 
@@ -25,6 +25,9 @@ ifeq ($(HASH),SHA3)
   SIGN_OPTIONS+=--sha3
 endif
 
+# Include SHA256 module because it's implicitly needed by RSA
+WOLFCRYPT_OBJS+=./lib/wolfssl/wolfcrypt/src/sha256.o
+
 ## ARM
 ifeq ($(ARCH),ARM)
   CROSS_COMPILE:=arm-none-eabi-