Fix calling conventions in malloc_ctl.h

The Perl_malloc() etc. functions are *also* declared in
proto.h, so the declarations need to match.  The inclusion
of malloc_ctl.h into perl.h had to be moved down until
after the point where PERL_CALLCONV was completely defined.

malloc_ctl.h

@@ -14,14 +14,12 @@ struct perl_mstats {
 };
 typedef struct perl_mstats perl_mstats_t;
 
-START_EXTERN_C
-Malloc_t Perl_malloc (MEM_SIZE nbytes);
-Malloc_t Perl_calloc (MEM_SIZE elements, MEM_SIZE size);
-Malloc_t Perl_realloc (Malloc_t where, MEM_SIZE nbytes);
+PERL_CALLCONV Malloc_t Perl_malloc (MEM_SIZE nbytes);
+PERL_CALLCONV Malloc_t Perl_calloc (MEM_SIZE elements, MEM_SIZE size);
+PERL_CALLCONV Malloc_t Perl_realloc (Malloc_t where, MEM_SIZE nbytes);
 /* 'mfree' rather than 'free', since there is already a 'perl_free'
  * that causes clashes with case-insensitive linkers */
-Free_t   Perl_mfree (Malloc_t where);
-END_EXTERN_C
+PERL_CALLCONV Free_t   Perl_mfree (Malloc_t where);
 
 #ifndef NO_MALLOC_DYNAMIC_CFG
 

perl.h

@@ -2387,10 +2387,6 @@ int isnan(double d);
 
 #endif
 
-#ifdef MYMALLOC
-#  include "malloc_ctl.h"
-#endif
-
 struct RExC_state_t;
 struct _reg_trie_data;
 
@@ -4979,6 +4975,10 @@ struct tempsym; /* defined in pp_pack.c */
 #define PERL_CKDEF(s)	PERL_CALLCONV OP *s (pTHX_ OP *o);
 #define PERL_PPDEF(s)	PERL_CALLCONV OP *s (pTHX);
 
+#ifdef MYMALLOC
+#  include "malloc_ctl.h"
+#endif
+
 #include "proto.h"
 
 /* this has structure inits, so it cannot be included before here */