environ variable from C runtime is not declared on all systems

compat.h

@@ -5,6 +5,10 @@
 #ifndef __compat_h_included
 #define __compat_h_included 1
 
+#if !HAVE_DECL_ENVIRON && HAVE_VAR_ENVIRON
+extern char **environ;
+#endif
+
 /*****************************************************************************/
 /* I dont like this system dependent part, but it would be quite a challenge
    for configure */

config.h.in

@@ -53,6 +53,13 @@
 /* Define if you have the putenv function.  */
 #undef HAVE_PUTENV
 
+/* Define if your cc provides char **environ declaration.
+   This implies HAVE_VAR_ENVIRON */
+#undef HAVE_DECL_ENVIRON
+
+/* Define if you have the char **environ variable */
+#undef HAVE_VAR_ENVIRON
+
 /* Define if you have the select function.  */
 #undef HAVE_SELECT
 

configure.in

@@ -1899,6 +1899,29 @@ if test -n "$WITH_FIPS"; then
 fi
 AC_SUBST(FIPSLD_CC)
 
+# autoconf does not seem to provide AC_CHECK_VAR or so
+# thus we have to check by foot
+AC_MSG_CHECKING(for declaration of environ)
+AC_CACHE_VAL(sc_cv_decl_environ,
+[AC_TRY_COMPILE([#include <unistd.h>],[char **s = environ;],
+[sc_cv_decl_environ=yes],
+[sc_cv_decl_environ=no])])
+if test $sc_cv_decl_environ = yes; then
+   AC_DEFINE(HAVE_DECL_ENVIRON)
+fi
+AC_MSG_RESULT($sc_cv_decl_environ)
+
+# on some systems environ exists but not the declaration
+AC_MSG_CHECKING(for var environ)
+AC_CACHE_VAL(sc_cv_var_environ,
+[AC_TRY_COMPILE([],[extern char **environ; char **s = environ;],
+[sc_cv_var_environ=yes],
+[sc_cv_var_environ=no])])
+if test $sc_cv_var_environ = yes; then
+   AC_DEFINE(HAVE_VAR_ENVIRON)
+fi
+AC_MSG_RESULT($sc_cv_var_environ)
+
 # allow BUILD_DATE to be externally set for build reproducibility
 if test "$BUILD_DATE"; then
   AC_DEFINE_UNQUOTED(BUILD_DATE, ["$BUILD_DATE"])

xio-openssl.c

@@ -1155,6 +1155,7 @@ static int openssl_delete_cert_info(void) {
    for (i = 0; i < l; ++i)  envprefix[i] = toupper(envprefix[i]);
    strncat(envprefix+l, "_OPENSSL_", XIO_ENVNAMELEN-l-1);
 
+#if HAVE_VAR_ENVIRON
    entry = (const char **)environ;
    while (*entry != NULL) {
       if (!strncmp(*entry, envprefix, strlen(envprefix))) {
@@ -1166,6 +1167,7 @@ static int openssl_delete_cert_info(void) {
 	 ++entry;
       }
    }
+#endif /* HAVE_VAR_ENVIRON */
    return 0;
 }