patch 9.1.0298: MS-Windows: GETTEXT_PATH hard-coded in src/po/Make_mvc.mak

Problem:  MS-Windows: GETTEXT_PATH hard-coded in src/po/Make_mvc.mak
Solution: Add IFNDEF/ENDIF around the definition of GETTEXT_PATH
          (Cthulhux)

It makes no sense to enforce modifying Vim source files just because
your build stuff is not where it's expected. My change is supposed to
add support for a locally-defined %GETTEXT_PATH%.

closes: #14480

Signed-off-by: Cthulhux <github@tuxproject.de>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/po/Make_mvc.mak b/src/po/Make_mvc.mak
index fa6a1ba..a9a69fd 100644
--- a/src/po/Make_mvc.mak
+++ b/src/po/Make_mvc.mak
@@ -44,7 +44,9 @@
 
 # Correct the following line for the directory where gettext et al is
 # installed.  Please do not put the path in quotes.
+!IFNDEF GETTEXT_PATH
 GETTEXT_PATH = D:\Programs\GetText\bin
+!ENDIF
 
 # Starting from version 0.22, msgfmt forcibly converts text to UTF-8 regardless
 # of the value of the "charset" field.