Use UTF-8 for saving wxTextCtrl contents now.

This ensures that the files created by wxTextCtrl::SaveFile() can be read back
by wxTextCtrl::LoadFile() as previously the files were saved using the current
locale encoding but read back using Latin1 (after first trying, and failing,
to read them as UTF-8).

This is a backwards incompatible change but it ensures that wxTextCtrl can
load its own files and is also consistent with the use of UTF-8 by default in
other places. Finally, and perhaps most importantly, this ensures that the
file contents can always be saved, i.e. there is no risk of conversion errors
any more.

Closes #15611.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75073 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Make windres command used in MinGW build configurable.

This allows to pass extra arguments to windres, which is especially important
when using 64 bit windres for building 32 bit applications as the generated .o
file uses a wrong architecture unless "-F pe-i386" is explicitly specified.

See #15601.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75074 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775