RetainerProfile.c: include missing header (#8810)

Found by clang:

  rts_dist_HC rts/dist/build/RetainerProfile.p_o

  rts/RetainerProfile.c:1779:5:
     error: implicit declaration of function 'markStableTables' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        markStableTables(retainRoot, NULL);
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Signed-off-by: Austin Seipp <austin@well-typed.com>

rts/RetainerProfile.c

@@ -30,6 +30,7 @@
 #include "Stats.h"
 #include "ProfHeap.h"
 #include "Apply.h"
+#include "Stable.h" /* markStableTables */
 #include "sm/Storage.h" // for END_OF_STATIC_LIST
 
 /*