Add gcem (#1928)

I'm aware it uses an unstable archive, but the project doesn't publish
anything else.

Co-authored-by: Caleb Zulawski <caleb.zulawski@caci.com>

modules/gcem/1.18.0/MODULE.bazel

@@ -0,0 +1,5 @@
+module(
+    name = "gcem",
+    version = "1.18.0",
+    compatibility_level = 0,
+)

modules/gcem/1.18.0/patches/add_build_file.patch

@@ -0,0 +1,9 @@
+--- /dev/null
++++ BUILD.bazel
+@@ -0,0 +1,6 @@
++cc_library(
++    name = "gcem",
++    hdrs = glob(["include/**/*"]),
++    strip_include_prefix = "/include",
++    visibility = ["//visibility:public"],
++)

modules/gcem/1.18.0/patches/module_dot_bazel.patch

@@ -0,0 +1,8 @@
+--- MODULE.bazel
++++ MODULE.bazel
+@@ -0,0 +1,5 @@
++module(
++    name = "gcem",
++    version = "1.18.0",
++    compatibility_level = 0,
++)

modules/gcem/1.18.0/presubmit.yml

@@ -0,0 +1,13 @@
+matrix:
+  platform:
+  - ubuntu2004
+  bazel:
+  - 7.x
+  - 6.x
+tasks:
+  verify_targets:
+    name: Verify build targets
+    platform: ${{ platform }}
+    bazel: ${{ bazel }}
+    build_targets:
+    - '@gcem//:gcem'

modules/gcem/1.18.0/source.json

@@ -0,0 +1,10 @@
+{
+    "url": "https://github.com/kthohr/gcem/archive/refs/tags/v1.18.0.tar.gz",
+    "integrity": "sha256-jnGp9bYpVtpsQJ3aRLSD+YxKmK5yGE86pGWa5bNGLmE=",
+    "strip_prefix": "gcem-1.18.0",
+    "patches": {
+        "module_dot_bazel.patch": "sha256-gQhcUru849j1GdyDdZFydgY1AM/nnOPHVUzSJqJbym8=",
+        "add_build_file.patch": "sha256-n3uNdOMc5GBjM4nOG0+8+WfttmeZgJFEtOrex8QFiaA="
+    },
+    "patch_strip": 0
+}

modules/gcem/metadata.json

@@ -0,0 +1,17 @@
+{
+    "homepage": "https://gcem.readthedocs.io/",
+    "maintainers": [
+        {
+            "email": "caleb.zulawski@gmail.com",
+            "github": "calebzulawski",
+            "name": "Caleb Zulawski"
+        }
+    ],
+    "repository": [
+        "github:kthohr/gcem"
+    ],
+    "versions": [
+        "1.18.0"
+    ],
+    "yanked_versions": {}
+}