Silence Apple Accelerate header warnings via system_header pragma

Apple's Accelerate/LAPACK/Sparse headers (pulled in through
ACCELERATE_NEW_LAPACK) trip a large, SDK-version-dependent set of
-Wpedantic/GNU-extension warnings: _Nullable/_Nonnull nullability
qualifiers, zero-arg variadic macros, extra semicolons, and more. On the
Xcode SDK this floods the build with tens of thousands of warnings from
headers we cannot fix.

Mark the Accelerate include as a system header with
`#pragma clang system_header` so all of its warnings are suppressed
regardless of which flag or SDK version produces them, while our own code
keeps full -Wpedantic strictness. cblas_wrapper.h contains nothing but
the include, so the marker is effectively scoped to Accelerate.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: dance858

include/utils/cblas_wrapper.h

@@ -20,6 +20,14 @@
 
 #ifdef __APPLE__
 #define ACCELERATE_NEW_LAPACK
+/* Apple's Accelerate/LAPACK/Sparse headers trip a large, SDK-dependent set
+ * of -Wpedantic/GNU-extension warnings (nullability qualifiers, zero-arg
+ * variadic macros, etc.) that we cannot fix and do not want in our build
+ * output. Treat everything included below as a system header so all of its
+ * warnings are suppressed, while our own code keeps full -Wpedantic
+ * strictness. This file contains nothing but the include, so the marker is
+ * effectively scoped to Accelerate. */
+#pragma clang system_header
 #include <Accelerate/Accelerate.h>
 #else
 #include <cblas.h>