Add wxProcess::SetPriority() to allow setting the priority of child processes.

This uses the same conventions as wxThread::SetPriority() but works on the
entire process.

Closes #14931.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73406 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/unix/threadpsx.cpp

@@ -58,10 +58,13 @@
     #include <cxxabi.h>
 #endif
 
+#ifdef HAVE_SETPRIORITY
+    #include <sys/resource.h>   // for setpriority()
+#endif
+
 // we use wxFFile under Linux in GetCPUCount()
 #ifdef __LINUX__
     #include "wx/ffile.h"
-    #include <sys/resource.h>   // for setpriority()
 #endif
 
 #define THR_ID_CAST(id)  (reinterpret_cast<void*>(id))