Allow {WINE,WINESERVER}_BIN env vars

Make it possible to set `WINE_BIN` and `WINESERVER_BIN` using
environment variables outside Winetricks. These affect binary bitness
detection during startup.

Winetricks performs a Wine binary bitness detection to print a warning.
In some environments such as Protontricks and Nix, the Wine executables are
wrappers that call binaries that are located elsewhere. In those
situations we want to provide the path to the binary that's only used
for the check to avoid printing unnecessary warnings.

Closes: #2183

src/winetricks

@@ -4402,7 +4402,13 @@ winetricks_set_wineprefix()
     if test -d "${W_DRIVE_C}/windows/syswow64"; then
         # Check the bitness of wineserver + wine binary, used later to determine if we're on a WOW setup (no wine64)
         # https://github.com/Winetricks/winetricks/issues/2030
-        WINESERVER_BIN="$(command -v "${WINESERVER}")"
+        # WINE_BIN and WINESERVER_BIN can be set outside Winetricks in case
+        # the `wine` and `wineserver` executables and the actual Wine binaries
+        # are located in different locations (usually the case for wrappers);
+        # this helps to avoid spurious "unknown file arch" warnings.
+        if [ -z "${WINESERVER_BIN}" ]; then
+            WINESERVER_BIN="$(command -v "${WINESERVER}")"
+        fi
 
         # wineboot often is a link pointing to wineapploader in Wine's bindir. If we don't find binaries we may look for them there later
         if [ -n "${READLINK_F}" ]; then
@@ -4436,7 +4442,9 @@ winetricks_set_wineprefix()
             w_warn "Unknown file arch of ${WINESERVER_BIN}."
         fi
 
-        WINE_BIN="$(command -v "${WINE}")"
+        if [ -z "${WINE_BIN}" ]; then
+            WINE_BIN="$(command -v "${WINE}")"
+        fi
         _W_wine_binary_arch="$(winetricks_get_file_arch "${WINE_BIN}")"
         if [ -z "${_W_wine_binary_arch}" ]; then
             # wine might be a script calling a binary in Wine's bindir.