Simplify khronos_api patch for Bazel build

Use relative paths to CARGO_MANIFEST_DIR in build.rs. Patch is
also submitted upstream at brendanzab/gl-rs#549

examples/bazel_build/MODULE.bazel

@@ -51,12 +51,8 @@ crate.spec(package = "slint-build", git = "https://github.com/slint-ui/slint", b
 
 crate.annotation(
     crate = "khronos_api",
-    patches = ["@//external_crate_builds:khronos_apis_fix_build.patch"],
+    patches = ["@//external_crate_builds:0001-Fix-build-with-Bazel.patch"],
     patch_args = ["-p1"],
-    compile_data = [":webgl_exts_rs"],
-    gen_build_script = "off",
-    additive_build_file = "@//external_crate_builds:khronos_api_webgl_exts_rs.BUILD.bazel",
-    rustc_env = {"WEBGL_EXTS": "$(location :webgl_exts_rs)"},
 )
 crate.annotation(
     crate = "proc-macro-crate",

examples/bazel_build/external_crate_builds/0001-Fix-build-with-Bazel.patch

@@ -0,0 +1,50 @@
+# Copyright © 2025 SixtyFPS GmbH
+# SPDX-License-Identifier: MIT
+
+# See https://github.com/brendanzab/gl-rs/pull/549
+
+From ff5fd1fa0a2416ddff942173d047e95979aa6dfd Mon Sep 17 00:00:00 2001
+From: Simon Hausmann <[email protected]>
+Date: Sun, 5 Jan 2025 10:43:59 +0100
+Subject: [PATCH] Fix build with Bazel
+
+When building Rust applications with Bazel instead of cargo, typically a
+sandbox is in place, where each process invocation (rustc, build.rs
+program, etc.) runs in its own "root", where the view on the filesystem
+is the same, but the absolute paths are different. As a consequence,
+CARGO_MANIFEST_DIR differs between the invocation of build.rs and rustc.
+
+That means that absolute paths in the generated webgl_exts.rs don't
+work. Fortunately, the source files are relative to the
+CARGO_MANIFEST_DIR, which, while changing between invocations, remains
+valid.
+---
+ khronos_api/build.rs | 5 +++--
+ 1 file changed, 3 insertions(+), 2 deletions(-)
+
+diff --git a/khronos_api/build.rs b/khronos_api/build.rs
+index 160179b..f7fc439 100644
+--- a/build.rs
++++ b/build.rs
+@@ -29,7 +29,8 @@ fn main() {
+     // The absolute path is needed, because we don't know where the output
+     // directory will be, and `include_bytes!(..)` resolves paths relative to the
+     // containing file.
+-    let root = env::current_dir().unwrap().join("api_webgl/extensions");
++    let cargo_manifest_dir = PathBuf::from(std::env::var_os("CARGO_MANIFEST_DIR").unwrap());
++    let root = cargo_manifest_dir.join("api_webgl/extensions");
+
+     // Generate a slice literal, looking like this:
+     // `&[&*include_bytes!(..), &*include_bytes!(..), ..]`
+@@ -53,7 +54,7 @@ fn main() {
+             let ext_path = path.join("extension.xml");
+             if ext_path.is_file() {
+                 // Include the XML file, making sure to use an absolute path.
+-                writeln!(file, "&*include_bytes!({:?}),", ext_path.to_str().unwrap()).unwrap();
++                writeln!(file, "&*include_bytes!(concat!(env!(\"CARGO_MANIFEST_DIR\"), \"/\", {:?})),", ext_path.strip_prefix(cargo_manifest_dir.clone()).unwrap().to_str().unwrap()).unwrap();
+             }
+         }
+     }
+-- 
+2.39.5 (Apple Git-154)
+