intel/compiler: Use INTEL_DEBUG=cs to ask for brw_compiler output

This removes output like

```
CS SIMD16 shader: 2790 inst, 0 loops, 24804 cycles, 166:106 spills:fills, 35 sends,
  scheduled with mode top-down, Promoted 1 constants, compacted 44640 to 41424 bytes.
```

from the default builds.  Like other debug output in intel_clc, they can
re-enabled with INTEL_DEBUG=cs.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26939>

src/intel/compiler/intel_clc.c

@@ -87,7 +87,8 @@ compiler_log(void *data, unsigned *id, const char *fmt, ...)
 {
    va_list args;
    va_start(args, fmt);
-   vfprintf(stderr, fmt, args);
+   if (INTEL_DEBUG(DEBUG_CS))
+      vfprintf(stderr, fmt, args);
    va_end(args);
 }