FEXRootFSFetcher: Check if curl is installed and fail before running

Before doing anything that requires curl, actually check if it is
installed.
Then instruct the user to install curl before using.

Doesn't try installing curl itself since we don't have a clean way to
execute sudo from potentially GUI.

Fixes #1498

Source/Tools/FEXRootFSFetcher/Main.cpp

@@ -809,6 +809,19 @@ int main(int argc, char **argv, char **const envp) {
     return 0;
   }
 
+  // Check if curl exists on the host
+  std::vector<const char*> ExecveArgs = {
+    "curl",
+    "-V",
+    nullptr,
+  };
+
+  int32_t Result = Exec::ExecAndWaitForResponseRedirect(ExecveArgs[0], const_cast<char* const*>(ExecveArgs.data()), -1, -1);
+  if (Result == -1) {
+    ExecWithInfo("curl is required to use this tool. Please install curl before using.");
+    return -1;
+  }
+
   FEX_CONFIG_OPT(LDPath, ROOTFS);
 
   std::error_code ec;