Split up mp_rand_source.c

In order to make `helper.pl` happy, change the ternary operator to an
if-else statement, otherwise it won't properly generate `tommath_class.h`.

This fixes #582
This closes #583

Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>

Author: sjaeckel

mp_rand_source.c

@@ -1,12 +1,12 @@
 #include "tommath_private.h"
-#ifdef MP_RAND_C
+#ifdef MP_RAND_SOURCE_C
 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
 /* SPDX-License-Identifier: Unlicense */
-
-mp_err(*s_mp_rand_source)(void *out, size_t size) = s_mp_rand_platform;
-
 void mp_rand_source(mp_err(*source)(void *out, size_t size))
 {
-   s_mp_rand_source = (source == NULL) ? s_mp_rand_platform : source;
+   if (source == NULL)
+      s_mp_rand_source = s_mp_rand_platform;
+   else
+      s_mp_rand_source = source;
 }
 #endif

s_mp_rand_source.c

@@ -0,0 +1,7 @@
+#include "tommath_private.h"
+#ifdef S_MP_RAND_SOURCE_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+mp_err(*s_mp_rand_source)(void *out, size_t size) = s_mp_rand_platform;
+#endif