if the system supports execvpe, use it so we don't have to hardcode the
paths to tools (which might move around)

https://bugs.gentoo.org/407195

--- a/configure.ac
+++ b/configure.ac
@@ -252,32 +252,19 @@ AC_ARG_WITH(pkcs11-helper-lib,
 
 AC_ARG_WITH(ifconfig-path,
    [  --with-ifconfig-path=PATH   Path to ifconfig tool],
-   [IFCONFIG="$withval"],
-   [AC_PATH_PROG([IFCONFIG], [ifconfig], [ifconfig], [$PATH:/usr/local/sbin:/usr/sbin:/sbin])]
 )
-AC_DEFINE_UNQUOTED(IFCONFIG_PATH, "$IFCONFIG", [Path to ifconfig tool])
 
 AC_ARG_WITH(iproute-path,
    [  --with-iproute-path=PATH    Path to iproute tool],
-   [IPROUTE="$withval"],
-   [AC_PATH_PROG([IPROUTE], [ip], [ip], [$PATH:/usr/local/sbin:/usr/sbin:/sbin])]
 )
-AC_DEFINE_UNQUOTED(IPROUTE_PATH, "$IPROUTE", [Path to iproute tool])
-
 
 AC_ARG_WITH(route-path,
    [  --with-route-path=PATH  Path to route tool],
-   [ROUTE="$withval"],
-   [AC_PATH_PROG([ROUTE], [route], [route], [$PATH:/usr/local/sbin:/usr/sbin:/sbin])]
 )
-AC_DEFINE_UNQUOTED(ROUTE_PATH, "$ROUTE", [Path to route tool])
 
 AC_ARG_WITH(netstat-path,
    [  --with-netstat-path=PATH  Path to netstat tool],
-   [NETSTAT="$withval"],
-   [AC_PATH_PROG([NETSTAT], [netstat], [netstat], [$PATH:/usr/local/sbin:/usr/sbin:/sbin:/etc])]
 )
-AC_DEFINE_UNQUOTED(NETSTAT_PATH, "$NETSTAT", [Path to netstat tool])
 
 AC_ARG_WITH(mem-check,
    [  --with-mem-check=TYPE  Build with debug memory checking, TYPE = dmalloc or valgrind],
@@ -499,7 +486,7 @@ AC_CHECK_FUNCS(daemon chroot getpwnam setuid nice system getpid dup dup2 dnl
 	       getpass strerror syslog openlog mlockall getgrnam setgid dnl
 	       setgroups stat flock readv writev time dnl
 	       setsid chdir putenv getpeername unlink dnl
-	       chsize ftruncate execve getpeereid umask)
+	       chsize ftruncate execve execvpe getpeereid umask)
 
 # Windows use stdcall for winsock so we cannot auto detect these
 m4_define([SOCKET_FUNCS], [socket recv recvfrom send sendto listen dnl
@@ -880,6 +867,26 @@ if test "$SELINUX" = "yes"; then
    )
 fi
 
+dnl
+dnl setup paths to tools as need be
+dnl
+AC_DEFUN([NET_TOOL],[dnl
+	AS_IF([test "x${with_$2_path}" != x],[dnl
+		$1=${with_$2_path}
+	],[dnl
+		AS_IF([test "x${ac_cv_func_execvpe}" = "xyes"],[dnl
+			$1=$2
+		],[dnl
+			AC_PATH_PROG($1, $2, $2, [$PATH:/usr/local/sbin:/usr/sbin:/sbin])
+		])
+	])
+	AC_DEFINE_UNQUOTED($1_PATH, "[$]$1", [Path to $2 tool])
+])
+NET_TOOL([IFCONFIG], [ifconfig])
+NET_TOOL([IPROUTE], [ip])
+NET_TOOL([ROUTE], [route])
+NET_TOOL([NETSTAT], [netstat])
+
 TAP_ID="PRODUCT_TAP_ID"
 TAP_WIN32_MIN_MAJOR="PRODUCT_TAP_WIN32_MIN_MAJOR"
 TAP_WIN32_MIN_MINOR="PRODUCT_TAP_WIN32_MIN_MINOR"
--- a/misc.c
+++ b/misc.c
@@ -521,7 +521,7 @@ openvpn_execve (const struct argv *a, const struct env_set *es, const unsigned i
 	      pid = fork ();
 	      if (pid == (pid_t)0) /* child side */
 		{
-		  execve (cmd, argv, envp);
+		  ENABLE_EXECVE (cmd, argv, envp);
 		  exit (127);
 		}
 	      else if (pid < (pid_t)0) /* fork failed */
--- a/syshead.h
+++ b/syshead.h
@@ -460,8 +460,12 @@ socket_defined (const socket_descriptor_t sd)
  * Should we enable the use of execve() for calling subprocesses,
  * instead of system()?
  */
-#if defined(HAVE_EXECVE) && defined(HAVE_FORK)
-#define ENABLE_EXECVE
+#if defined(HAVE_FORK)
+# if defined(HAVE_EXECVPE)
+#  define ENABLE_EXECVE execvpe
+# elif defined(HAVE_EXECVE)
+#  define ENABLE_EXECVE execve
+# endif
 #endif
 
 /*