rusticl: Add RUSTICL_FEATURES=intel

We're going to hide some of the cl_intel_* extensions behind that until
they start stabilizing.

Acked-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31772>

docs/envvars.rst

@@ -1188,6 +1188,7 @@ Rusticl environment variables
 
    - ``fp16`` enables OpenCL half support
    - ``fp64`` enables OpenCL double support
+   - ``intel`` enables various Intel OpenCL extensions
 
 .. envvar:: RUSTICL_DEBUG
 

src/gallium/frontends/rusticl/core/platform.rs

@@ -46,6 +46,7 @@ pub struct PlatformDebug {
 pub struct PlatformFeatures {
     pub fp16: bool,
     pub fp64: bool,
+    pub intel: bool,
 }
 
 static PLATFORM_ENV_ONCE: Once = Once::new();
@@ -72,6 +73,7 @@ static mut PLATFORM_DBG: PlatformDebug = PlatformDebug {
 static mut PLATFORM_FEATURES: PlatformFeatures = PlatformFeatures {
     fp16: false,
     fp64: false,
+    intel: false,
 };
 
 fn load_env() {
@@ -108,6 +110,7 @@ fn load_env() {
             match flag {
                 "fp16" => features.fp16 = true,
                 "fp64" => features.fp64 = true,
+                "intel" => features.intel = true,
                 "" => (),
                 _ => eprintln!("Unknown RUSTICL_FEATURES flag found: {}", flag),
             }