Upgrade to m4 1.4.19

This version includes the patch at bazel/m4.patch and fixes an additional build failure related to SIGSTKSZ, allowing ZetaSQL to build on Ubuntu 21.10.

https://lore.kernel.org/all/e3521179-8f13-2628-6f30-6480c5795bf5@mind.be/T/

```
diff --git a/bazel/zetasql_deps_step_2.bzl b/bazel/zetasql_deps_step_2.bzl
index 4ba0e96..e4d0808 100644
--- a/bazel/zetasql_deps_step_2.bzl
+++ b/bazel/zetasql_deps_step_2.bzl
@@ -460,13 +460,13 @@ exports_files(["data"])
http_archive(
name = "m4",
build_file_content = all_content,
- strip_prefix = "m4-1.4.18",
- sha256 = "ab2633921a5cd38e48797bf5521ad259bdc4b979078034a3b790d7fec5493fab",
+ strip_prefix = "m4-1.4.19",
+ sha256 = "63aede5c6d33b6d9b13511cd0be2cac046f2e70fd0a07aa9573a04a82783af96",
urls = [
- "https://ftp.gnu.org/gnu/m4/m4-1.4.18.tar.gz",
- "https://mirrors.kernel.org/gnu/m4/m4-1.4.18.tar.gz",
+ "https://ftp.gnu.org/gnu/m4/m4-1.4.19.tar.xz",
+ "https://mirrors.kernel.org/gnu/m4/m4-1.4.19.tar.xz",
],
- patches = ["@com_google_zetasql//bazel:m4.patch"],
)

http_archive(
```