diff --git gcl/configure gcl/configure
index 2f4063f60..bfeaa2ca2 100755
--- configure
+++ configure
@@ -8166,6 +8166,7 @@ else $as_nop
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+		    #include <unistd.h>
 		    #include <stdio.h>
 		    #include <stdlib.h>
 		    int main(int argc,char *argv[],char *envp[]) {
@@ -8203,6 +8204,7 @@ else $as_nop
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+		    #include <unistd.h>
 		    #include <stdio.h>
 		    #include <stdlib.h>
 		    int main(int argc,char * argv[],char * envp[]) {
@@ -8240,6 +8242,7 @@ else $as_nop
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+		    #include <unistd.h>
 		    #include <stdio.h>
 		    #include <stdlib.h>
 		    int main(int argc,char * argv[],char * envp[]) {
@@ -8290,6 +8293,7 @@ else $as_nop
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+		#include <unistd.h>
 		#include <stdio.h>
 		#include <stdlib.h>
 		int main(int argc,char **argv,char **envp) {
@@ -8330,6 +8334,7 @@ else $as_nop
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+		#include <unistd.h>
 		#include <stdio.h>
 		#include <stdlib.h>
 		int main(int argc,char **argv,char **envp) {
@@ -8386,6 +8391,7 @@ else $as_nop
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+		#include <unistd.h>
 		#include <stdio.h>
 		#include <stdlib.h>
 		int
@@ -8437,6 +8443,7 @@ else $as_nop
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+		#include <unistd.h>
 		#include <stdio.h>
 		#include <stdlib.h>
 		int
@@ -8490,6 +8497,7 @@ else $as_nop
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+		#include <unistd.h>
 		#include <stdio.h>
 		#include <stdlib.h>
 		int
diff --git configure.in configure.in
index 55ace8eaf..ce7c1fb8e 100644
--- configure.in
+++ configure.in
@@ -1238,6 +1238,7 @@ if test "$HAVE_SBRK" = "1" ; then
     AC_RUN_IFELSE(
 	[AC_LANG_SOURCE(
 		[[
+		    #include <unistd.h>
 		    #include <stdio.h>
 		    #include <stdlib.h>
 		    int main(int argc,char *argv[],char *envp[]) {
@@ -1254,6 +1255,7 @@ if test "$HAVE_SBRK" = "1" ; then
     AC_RUN_IFELSE(
 	[AC_LANG_SOURCE(
 		[[
+		    #include <unistd.h>
 		    #include <stdio.h>
 		    #include <stdlib.h>
 		    int main(int argc,char * argv[],char * envp[]) {
@@ -1275,6 +1277,7 @@ if test "$HAVE_SBRK" = "1" ; then
     AC_RUN_IFELSE(
 	[AC_LANG_SOURCE(
 		[[
+		    #include <unistd.h>
 		    #include <stdio.h>
 		    #include <stdlib.h>
 		    int main(int argc,char * argv[],char * envp[]) {
@@ -1306,6 +1309,7 @@ AC_MSG_CHECKING(CSTACK_DIRECTION)
 AC_RUN_IFELSE(
     [AC_LANG_SOURCE(
 	    [[
+		#include <unistd.h>
 		#include <stdio.h>
 		#include <stdlib.h>
 		int main(int argc,char **argv,char **envp) {
@@ -1325,6 +1329,7 @@ AC_MSG_CHECKING([finding CSTACK_ALIGNMENT])
 AC_RUN_IFELSE(
     [AC_LANG_SOURCE(
 	    [[
+		#include <unistd.h>
 		#include <stdio.h>
 		#include <stdlib.h>
 		int main(int argc,char **argv,char **envp) {
@@ -1354,6 +1359,7 @@ AC_MSG_CHECKING(CSTACK_ADDRESS)
 AC_RUN_IFELSE(
     [AC_LANG_SOURCE(
 	    [[
+		#include <unistd.h>
 		#include <stdio.h>
 		#include <stdlib.h>
 		int
@@ -1384,6 +1390,7 @@ AC_MSG_CHECKING([cstack bits])
 AC_RUN_IFELSE(
     [AC_LANG_SOURCE(
 	    [[
+		#include <unistd.h>
 		#include <stdio.h>
 		#include <stdlib.h>
 		int
@@ -1416,6 +1423,7 @@ AC_MSG_CHECKING(NEG_CSTACK_ADDRESS)
 AC_RUN_IFELSE(
     [AC_LANG_SOURCE(
 	    [[
+		#include <unistd.h>
 		#include <stdio.h>
 		#include <stdlib.h>
 		int