Force utf8 encoding for wxString in all Unix-like platforms

deps/wxWidgets/wxWidgets.cmake

@@ -9,6 +9,11 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
     set(_wx_toolkit "-DwxBUILD_TOOLKIT=gtk${_gtk_ver}")
 endif()
 
+set(_unicode_utf8 OFF)
+if (UNIX) # wxWidgets will not use char as the underlying type for wxString unless its forced to.
+    set (_unicode_utf8 ON)
+endif()
+
 prusaslicer_add_cmake_project(wxWidgets
     # GIT_REPOSITORY "https://github.com/prusa3d/wxWidgets"
     # GIT_TAG tm_cross_compile #${_wx_git_tag}
@@ -23,6 +28,7 @@ prusaslicer_add_cmake_project(wxWidgets
         -DwxUSE_MEDIACTRL=OFF
         -DwxUSE_DETECT_SM=OFF
         -DwxUSE_UNICODE=ON
+        -DwxUSE_UNICODE_UTF8=${_unicode_utf8}
         -DwxUSE_OPENGL=ON
         -DwxUSE_LIBPNG=sys
         -DwxUSE_ZLIB=sys