Update configure.ac

#include <unistd.h> no #include <process.h>
needed in linux, fixes make warning

configure.ac

@@ -295,12 +295,21 @@ fi
 AM_CONDITIONAL(USE_GIT_VERSION, [test x$usegitver = xyes])
 
 #check execv signature
+if test "x$have_linux" == xtrue; then
+    AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+           #include <unistd.h>
+           int execv(const char*, char *const*);
+           ])],
+           AC_DEFINE([EXECV_2ND_ARG_TYPE], [char* const*], [int execv(const char*, char*const*);]),
+           AC_DEFINE([EXECV_2ND_ARG_TYPE], [const char* const*], [int execv(const char*, const char*const*);]))
+else
     AC_COMPILE_IFELSE([AC_LANG_SOURCE([
            #include <process.h>
            int execv(const char*, char *const*);
            ])],
            AC_DEFINE([EXECV_2ND_ARG_TYPE], [char* const*], [int execv(const char*, char*const*);]),
            AC_DEFINE([EXECV_2ND_ARG_TYPE], [const char* const*], [int execv(const char*, const char*const*);]))
+fi
 
 dnl CCAN wants to know a lot of vars.
 # All the configuration checks.  Regrettably, the __attribute__ checks will