Fix GCC_LINUX_FUTEX to work with C99 compilers

Without this change, libstdc++ is built without futex symbols if GCC
rejects implicit function declarations by default.

From-SVN: r275454

config/ChangeLog

+2019-09-06  Florian Weimer  <fweimer@redhat.com>
+
+	* futex.m4 (GCC_LINUX_FUTEX): Include <unistd.h> for the syscall
+	function.
+
 2019-07-08  Richard Sandiford  <richard.sandiford@arm.com>
 
 	* bootstrap-Og.mk: New file.

config/futex.m4

@@ -22,6 +22,7 @@ case "$target" in
 	AC_LINK_IFELSE(
 	 [AC_LANG_PROGRAM(
 	  [#include <sys/syscall.h>
+	   #include <unistd.h>
 	   int lk;],
 	  [syscall (SYS_gettid); syscall (SYS_futex, &lk, 0, 0, 0);])],
 	  [save_LIBS="$LIBS"
@@ -48,6 +49,7 @@ If so, please configure with --disable-linux-futex])
 	AC_LINK_IFELSE(
 	 [AC_LANG_PROGRAM(
 	  [#include <sys/syscall.h>
+	   #include <unistd.h>
 	   int lk;],
 	  [syscall (SYS_gettid); syscall (SYS_futex, &lk, 0, 0, 0);])],[],
 	  [AC_MSG_ERROR([SYS_gettid and SYS_futex required for --enable-linux-futex])])

libgomp/ChangeLog

+2019-09-06  Florian Weimer  <fweimer@redhat.com>
+
+	* configure: Regenerate.
+
 2019-09-03  Chung-Lin Tang  <cltang@codesourcery.com>
 
 	PR other/79543

libgomp/configure

@@ -15888,6 +15888,7 @@ case "$target" in
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 #include <sys/syscall.h>
+	   #include <unistd.h>
 	   int lk;
 int
 main ()
@@ -15940,6 +15941,7 @@ rm -f core conftest.err conftest.$ac_objext \
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 #include <sys/syscall.h>
+	   #include <unistd.h>
 	   int lk;
 int
 main ()

libitm/ChangeLog

+2019-09-06  Florian Weimer  <fweimer@redhat.com>
+
+	* configure: Regenerate.
+
 2019-09-03  Chung-Lin Tang  <cltang@codesourcery.com>
 
 	PR other/79543

libitm/configure

@@ -16481,6 +16481,7 @@ case "$target" in
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 #include <sys/syscall.h>
+	   #include <unistd.h>
 	   int lk;
 int
 main ()
@@ -16533,6 +16534,7 @@ rm -f core conftest.err conftest.$ac_objext \
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 #include <sys/syscall.h>
+	   #include <unistd.h>
 	   int lk;
 int
 main ()

libstdc++-v3/ChangeLog

+2019-09-06  Florian Weimer  <fweimer@redhat.com>
+
+	* configure: Regenerate.
+
 2019-09-05  Jonathan Wakely  <jwakely@redhat.com>
 
 	* doc/xml/manual/status_cxx2020.xml: Update status for P0122R7 and

libstdc++-v3/configure

@@ -72670,6 +72670,7 @@ fi
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 #include <sys/syscall.h>
+	   #include <unistd.h>
 	   int lk;
 int
 main ()
@@ -72728,6 +72729,7 @@ fi
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 #include <sys/syscall.h>
+	   #include <unistd.h>
 	   int lk;
 int
 main ()