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_code11.c

@@ -55,7 +55,7 @@ static void test_large(const testCtx *const p_ctx) {
     int i, length, ret;
     struct zint_symbol *symbol = NULL;
 
-    char data_buf[4096];
+    char data_buf[4096] = {0}; /* Suppress clang -fsanitize=memory false positive */
 
     testStartSymbol("test_large", &symbol);