Merge pull request #5271 from gilles-peskine-arm/fix-builds-with-only-mbedtls_bignum_c-defined-2.16

Backport 2.16: Fix builds when config.h only defines MBEDTLS_BIGNUM_C

ChangeLog.d/build-without-sha.txt

@@ -0,0 +1,3 @@
+Bugfix
+   * Fix the build when no SHA2 module is included. Fixes #4930.
+   * Fix the build when only the bignum module is included. Fixes #4929.

include/mbedtls/entropy.h

@@ -157,7 +157,7 @@ typedef struct mbedtls_entropy_context
                               * -1 after free. */
 #if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
     mbedtls_sha512_context  accumulator;
-#else
+#elif defined(MBEDTLS_ENTROPY_SHA256_ACCUMULATOR)
     mbedtls_sha256_context  accumulator;
 #endif
     int             source_count; /* Number of entries used in source. */

library/bignum.c

@@ -72,6 +72,7 @@
 #include "mbedtls/bn_mul.h"
 #include "mbedtls/platform_util.h"
 
+#include <limits.h>
 #include <string.h>
 
 #if defined(MBEDTLS_PLATFORM_C)