Merge bitcoin/bitcoin#32567: subprocess: Backport upstream changes

e63a703 subprocess: Don't add an extra whitespace at end of Windows command line (laanwj)

Pull request description:

  A list of the backported PRs:
  - arun11299/cpp-subprocess#119

  The following PRs were skipped for backporting:
  - arun11299/cpp-subprocess#118 because there is no changes in the header code.

  Required for bitcoin/bitcoin#32566.

ACKs for top commit:
  laanwj:
    Code review ACK e63a703

Tree-SHA512: 69a74aa7f9c611a9ec910e27161c5e9e147067d37f8335953cd3875fcc88dc840a2f7b206bb603f22507159e406b1449f1dc4702fffe890bb824672641b4feed

Author: fanquake

src/util/subprocess.h

@@ -1124,11 +1124,16 @@ inline void Popen::execute_process() noexcept(false)
   std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> converter;
   std::wstring argument;
   std::wstring command_line;
+  bool first_arg = true;
 
   for (auto arg : this->vargs_) {
+    if (!first_arg) {
+      command_line += L" ";
+    } else {
+      first_arg = false;
+    }
     argument = converter.from_bytes(arg);
     util::quote_argument(argument, command_line, false);
-    command_line += L" ";
   }
 
   // CreateProcessW can modify szCmdLine so we allocate needed memory