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_library.c

@@ -1577,7 +1577,7 @@ static int test_prev_ZBarcode_BarcodeName(int symbol_id, char name[32]) {
 static void test_barcode_name(const testCtx *const p_ctx) {
 
     int ret;
-    char name[32];
+    char name[32] = {0}; /* Suppress clang -fsanitize=memory false positive */
     int symbol_id;
 
     (void)p_ctx;