general: cmake: add ZINT_SANITIZEM (clang -fsanitize=memory) option

and suppress errors in lib and backend tests (pretty sure they're
  nearly all false positives apart from maybe 2 non-initializations
  in "gif.c" (`pOut` buffer) and "raster.c" (`rotated_pixbuf`)
github: install de_DE.UTF-8 locale in ubuntu-debug also

backend/tests/test_pdf417.c

@@ -5762,7 +5762,7 @@ static void test_numbprocess(const testCtx *const p_ctx) {
     const int data_size = ARRAY_SIZE(data);
     int i, length;
 
-    short chainemc[32];
+    short chainemc[32] = {0}; /* Suppress clang -fsanitize=memory false positive */
     int mclength;
 
     testStart("test_numbprocess");