Adjust more modules to new design

Add `ecp.h` anf `timing.h` to new XXX_alt design

include/mbedtls/ecp.h

@@ -39,6 +39,10 @@
 #define MBEDTLS_ERR_ECP_SIG_LEN_MISMATCH                  -0x4C00  /**< Signature is valid but shorter than the user-supplied length. */
 #define MBEDTLS_ERR_ECP_HW_ACCEL_FAILED                   -0x4B80  /**< ECP hardware accelerator failed. */
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #if !defined(MBEDTLS_ECP_ALT)
 /*
  * default mbed TLS elliptic curve arithmetic implementation
@@ -48,10 +52,6 @@
  * one.)
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * Domain parameters (curve, subgroup and generator) identifiers.
  *
@@ -237,6 +237,10 @@ mbedtls_ecp_keypair;
 #define MBEDTLS_ECP_PF_UNCOMPRESSED    0   /**< Uncompressed point format */
 #define MBEDTLS_ECP_PF_COMPRESSED      1   /**< Compressed point format */
 
+#else  /* MBEDTLS_ECP_ALT */
+#include "ecp_alt.h"
+#endif /* MBEDTLS_ECP_ALT */
+
 /*
  * Some other constants from RFC 4492
  */
@@ -679,8 +683,4 @@ int mbedtls_ecp_self_test( int verbose );
 }
 #endif
 
-#else  /* MBEDTLS_ECP_ALT */
-#include "ecp_alt.h"
-#endif /* MBEDTLS_ECP_ALT */
-
 #endif /* ecp.h */

include/mbedtls/timing.h

@@ -30,16 +30,16 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
-#if !defined(MBEDTLS_TIMING_ALT)
-// Regular implementation
-//
-
 #include <stdint.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_TIMING_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          timer structure
  */
@@ -58,6 +58,10 @@ typedef struct
     uint32_t                        fin_ms;
 } mbedtls_timing_delay_context;
 
+#else  /* MBEDTLS_TIMING_ALT */
+#include "timing_alt.h"
+#endif /* MBEDTLS_TIMING_ALT */
+
 extern volatile int mbedtls_timing_alarmed;
 
 /**
@@ -133,18 +137,6 @@ void mbedtls_timing_set_delay( void *data, uint32_t int_ms, uint32_t fin_ms );
  */
 int mbedtls_timing_get_delay( void *data );
 
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_TIMING_ALT */
-#include "timing_alt.h"
-#endif /* MBEDTLS_TIMING_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #if defined(MBEDTLS_SELF_TEST)
 /**
  * \brief          Checkup routine