Take Cryptographic API outside the XXX_ALT check

The cryptographic API should not be related to whether or not
there is alternative implementation. The API should be same for regular
implementation, and for alternative implementation, so it is defined
outside of the XXX_ALT precompilation check in the cryptographic API header

include/mbedtls/md4.h

@@ -40,14 +40,14 @@
 
 #define MBEDTLS_ERR_MD4_HW_ACCEL_FAILED                   -0x002D  /**< MD4 hardware accelerator failed */
 
-#if !defined(MBEDTLS_MD4_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_MD4_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          MD4 context structure
  *
@@ -64,6 +64,10 @@ typedef struct
 }
 mbedtls_md4_context;
 
+#else  /* MBEDTLS_MD4_ALT */
+#include "md4_alt.h"
+#endif /* MBEDTLS_MD4_ALT */
+
 /**
  * \brief          Initialize MD4 context
  *
@@ -238,18 +242,6 @@ MBEDTLS_DEPRECATED void mbedtls_md4_process( mbedtls_md4_context *ctx,
 #undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_MD4_ALT */
-#include "md4_alt.h"
-#endif /* MBEDTLS_MD4_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * \brief          Output = MD4( input buffer )
  *