[gimp] build: make clearer mandatory installer-needed macros.

[Jehan <jehanp src gnome org>]

commit 4b9f7b25125e889fe5caa3891bc585cfa92cb3df
Author: Jehan <jehan girinstud io>
Date:   Sat Mar 19 13:48:37 2022 +0100

    build: make clearer mandatory installer-needed macros.
    
    Instead of replacing various needed macros with random hardcoded values,
    just make them mandatory and exit with explicit error when a needed
    macro is missing.

 build/windows/installer/gimp3264.iss | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)
---
diff --git a/build/windows/installer/gimp3264.iss b/build/windows/installer/gimp3264.iss
index 10d85fcf69..9af2891b85 100755
--- a/build/windows/installer/gimp3264.iss
+++ b/build/windows/installer/gimp3264.iss
@@ -80,20 +80,28 @@
 #pragma option -e+
 
 #ifndef VERSION
-       #define DEVEL "is6"
-       #define VERSION "2.10.12"
-       #define NOFILES
-       #define GIMP_DIR "W:\msys64-gtk2\opt\output\2.10.12"
-       #define DIR32 "i686-w64-mingw32"
-       #define DIR64 "x86_64-w64-mingw32" 
-       #define DEPS_DIR "W:\msys64-gtk2\opt\comb"
-       #define DDIR32 "mingw32"
-       #define DDIR64 "mingw64"
-       #define PYTHON
-       #define LUA
-       #define DEBUG_SYMBOLS
-       #define NOCOMPRESSION
+       #error VERSION must be defined
 #endif
+#ifndef GIMP_DIR
+       #error GIMP_DIR must be defined
+#endif
+#ifndef DIR32
+       #error DIR32 must be defined
+#endif
+#ifndef DIR64
+       #error DIR64 must be defined
+#endif
+#ifndef DEPS_DIR
+       #error DEPS_DIR must be defined
+#endif
+#ifndef DDIR32
+       #error DDIR32 must be defined
+#endif
+#ifndef DDIR64
+       #error DDIR64 must be defined
+#endif
+
+; Optional: PYTHON, LUA, DEBUG_SYMBOLS, NOCOMPRESSION, NOFILES, DEVEL
 
 #include "directories.isi"
 #include "version.isi"