move system_error out of common header

Author: CamJN

include/libgetargv++.hpp

@@ -9,7 +9,6 @@
 
 #include "iter.hpp"
 #include <string>
-#include <system_error>
 #include <vector>
 
 /** \brief This namespace isolates the library from your code.

src/argv.cpp

@@ -1,4 +1,5 @@
 #include "../include/libgetargv++.hpp"
+#include <system_error>
 
 namespace Getargv {
 
@@ -49,7 +50,7 @@ namespace Getargv {
   Argv::Argv(pid_t pid, unsigned int skip, bool nuls) noexcept(false) : ArgvResult() {
     ffi::GetArgvOptions const options = {
       #if defined(__cplusplus) && (__cplusplus >= 202002L)
-    .skip = static_cast<ffi::uint>(skip),
+      .skip = static_cast<ffi::uint>(skip),
       .pid  = pid,
       .nuls = nuls,
       #else

src/argvargc.cpp

@@ -1,5 +1,6 @@
 #include "../include/libgetargv++.hpp"
 #include <algorithm>
+#include <system_error>
 
 namespace Getargv {