[slog] Assume STDC_HEADERS is defined

* configure.ac (guile_cv_localtime_cache): Rewrite
preprocessor conditional block, assuming STDC_HEADERS is 1.

* libguile/gen-scmconfig.c (SCM_HAVE_STDC_HEADERS):
#define to 1 unconditionally.
Rewrite preprocessor conditional block,
assuming STDC_HEADERS is 1.
* libguile/putenv.c: Rewrite preprocessor conditional block,
assuming STDC_HEADERS is 1.

configure.ac

@@ -1080,9 +1080,7 @@ AC_MSG_CHECKING([whether localtime caches TZ])
 AC_CACHE_VAL([guile_cv_localtime_cache],
 [if test x$ac_cv_func_tzset = xyes; then
 AC_RUN_IFELSE([AC_LANG_SOURCE([[#include <time.h>
-#if STDC_HEADERS
 #include <stdlib.h>
-#endif
 extern char **environ;
 unset_TZ ()
 {

libguile/gen-scmconfig.c

@@ -157,7 +157,10 @@ main (int argc, char *argv[])
 #endif
 
   pf("\n");
-#ifdef STDC_HEADERS
+  /* The configure script used to check for and define STDC_HEADERS
+     conditionally.  Nowadays that is "obsolescent"
+     (info "(autoconf) Particular Headers")
+     but we define SCM_HAVE_STDC_HEADERS anyway for backward compat.  */
   pf ("#define SCM_HAVE_STDC_HEADERS 1 /* 0 or 1 */\n");
   pf ("#include <stdlib.h>\n");
 #if HAVE_SYS_TYPES_H
@@ -167,9 +170,6 @@ main (int argc, char *argv[])
   pf ("#include <sys/stdtypes.h>\n");
 #endif
   pf ("#include <stddef.h>\n");
-#else /* STDC_HEADERS */
-  pf ("#define SCM_HAVE_STDC_HEADERS 0 /* 0 or 1 */");
-#endif /* def STDC_HEADERS */
 
   pf("\n");
 #ifdef HAVE_SYS_SELECT_H

libguile/putenv.c

@@ -35,17 +35,7 @@
 char *malloc ();
 #endif	/* GNU C library.  */
 
-#if defined(STDC_HEADERS) || defined(HAVE_STRING_H)
 #include <string.h>
-#else
-#include <strings.h>
-#ifndef strchr
-#define strchr index
-#endif
-#ifndef memcpy
-#define memcpy(d, s, n) bcopy((s), (d), (n))
-#endif
-#endif
 
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>