Add error message for old armclang

when armclang<6.10, cpu modifiers MUST be
specified on command line.

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/sha256.c b/library/sha256.c
index 104fa80..5df61ac 100644
--- a/library/sha256.c
+++ b/library/sha256.c
@@ -70,11 +70,17 @@
 #   endif
 
 #    if !defined(__ARM_FEATURE_CRYPTO) || defined(MBEDTLS_ENABLE_ARM_CRYPTO_EXTENSIONS_COMPILER_FLAG)
-#      if defined(__clang__)
+#      if defined(__ARMCOMPILER_VERSION)
+#        if __ARMCOMPILER_VERSION <= 6090000
+#          error "Must use minimum -march=armv8-a+crypto for MBEDTLS_SHA256_USE_A64_CRYPTO_*"
+#        endif
+#          pragma clang attribute push (__attribute__((target("sha2"))), apply_to=function)
+#          define MBEDTLS_POP_TARGET_PRAGMA
+#      elif defined(__clang__)
 #        if __clang_major__ < 4
 #          error "A more recent Clang is required for MBEDTLS_SHA256_USE_A64_CRYPTO_*"
 #        endif
-#        pragma clang attribute push (__attribute__((target("crypto,sha2"))), apply_to=function)
+#        pragma clang attribute push (__attribute__((target("crypto"))), apply_to=function)
 #        define MBEDTLS_POP_TARGET_PRAGMA
 #      elif defined(__GNUC__)
          /* FIXME: GCC 5 claims to support Armv8 Crypto Extensions, but some