Fix checking for `wx-config` first on Gentoo.

Followup on 98b2fb6e.

To make a one element of empty string list in cmake, you have to set the
variable to `";"`.

If it is set to `""`, a subsequent `list(APPEND ...)` will consider the
variable unset.

With this fix, `/usr/bin/wx-config` is tried first on Gentoo, as was
intended in 98b2fb6e.

The rationale for this is that on Gentoo, app-eselect/eselect-wxwidgets
links `/usr/bin/wx-config` to the user's preferred version of wxWidgets,
while on other distributions such as Arch, we want to check for the 3.x
gtk3 variant explicitly first.

Also add a modeline to `VbamFunctions.cmake`.

Signed-off-by: Rafael Kitover <rkitover@gmail.com>

cmake/VbamFunctions.cmake

@@ -71,10 +71,13 @@ function(find_wx_util var util)
     if(WIN32 OR EXISTS /etc/gentoo-release)
         # On win32, including cross builds we prefer the plain utility name
         # first from PATH.
+        #
         # On Gentoo /usr/bin/wx-config loads the eselected build, so we want
         # to try that first.
-      set(conf_suffixes  "")
-      set(major_versions "")
+        #
+        # This makes a one element of empty string list.
+        set(conf_suffixes  ";")
+        set(major_versions ";")
     endif()
 
     list(APPEND conf_suffixes  gtk4u gtk4 gtk3u gtk3 gtk2u gtk2 "")
@@ -132,3 +135,5 @@ function(find_wx_util var util)
         set(${var} ${util} PARENT_SCOPE)
     endforeach()
 endfunction()
+
+# vim:sw=4 sts et: