Assume that we have memmove().

Windows has this, and so do all other live platforms according to the
buildfarm, so remove the configure probe and c.h's substitute code.

This is part of a series of commits to get rid of no-longer-relevant
configure checks and dead src/port/ code.  I'm committing them separately
to make it easier to back out individual changes if they prove less
portable than I expect.

Discussion: https://postgr.es/m/15379.1582221614@sss.pgh.pa.us

configure

@@ -14925,7 +14925,7 @@ fi
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-for ac_func in backtrace_symbols clock_gettime copyfile fdatasync getifaddrs getpeerucred getrlimit kqueue mbstowcs_l memset_s memmove poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open strchrnul strsignal symlink sync_file_range uselocale utime utimes wcstombs_l
+for ac_func in backtrace_symbols clock_gettime copyfile fdatasync getifaddrs getpeerucred getrlimit kqueue mbstowcs_l memset_s poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open strchrnul strsignal symlink sync_file_range uselocale utime utimes wcstombs_l
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"

configure.in

@@ -1627,7 +1627,6 @@ AC_CHECK_FUNCS(m4_normalize([
 	kqueue
 	mbstowcs_l
 	memset_s
-	memmove
 	poll
 	posix_fallocate
 	ppoll

src/include/c.h

@@ -1261,10 +1261,6 @@ extern long long strtoll(const char *str, char **endptr, int base);
 extern unsigned long long strtoull(const char *str, char **endptr, int base);
 #endif
 
-#if !defined(HAVE_MEMMOVE) && !defined(memmove)
-#define memmove(d, s, c)		bcopy(s, d, c)
-#endif
-
 /* no special DLL markers on most ports */
 #ifndef PGDLLIMPORT
 #define PGDLLIMPORT

src/include/pg_config.h.in

@@ -370,9 +370,6 @@
 /* Define to 1 if you have the `mbstowcs_l' function. */
 #undef HAVE_MBSTOWCS_L
 
-/* Define to 1 if you have the `memmove' function. */
-#undef HAVE_MEMMOVE
-
 /* Define to 1 if you have the <memory.h> header file. */
 #undef HAVE_MEMORY_H
 

src/tools/msvc/Solution.pm

@@ -294,7 +294,6 @@ sub GenerateFiles
 		HAVE_LONG_LONG_INT_64       => 1,
 		HAVE_MBARRIER_H             => undef,
 		HAVE_MBSTOWCS_L             => 1,
-		HAVE_MEMMOVE                => 1,
 		HAVE_MEMORY_H               => 1,
 		HAVE_MEMSET_S               => undef,
 		HAVE_MINIDUMP_TYPE          => 1,