Add ifdef for xnn_enable_avx512f and xnn_enable_avx512skx #415

Job	Run time
build-and-test / cmake-linux-x86_64	6m 30s
build-and-test / cmake-linux-aarch64	6m 22s
build-and-test / cmake-linux-armhf	5m 12s
build-and-test / cmake-linux-riscv64	3m 54s
build-and-test / cmake-linux-riscv64-rvv	4m 22s
build-and-test / cmake-windows-arm64	4m 24s
build-and-test / cmake-windows-x64	5m 18s
build-and-test / cmake-windows-x86	5m 52s
build-and-test / bazel-linux-x86_64-clang-18	5m 15s
build-and-test / cmake-android (arm64)	6m 14s
build-and-test / cmake-ios-arm64	7m 57s
build-and-test / cmake-android (armv7)	5m 40s
build-and-test / cmake-ios-x86_64	7m 7s
build-and-test / cmake-android (x86)	7m 11s
build-and-test / cmake-macos-arm64	7m 45s
build-and-test / bazel-linux-aarch64	9m 24s
build-and-test / bazel-linux-x86_64-gcc-9	5m 45s
	1h 44m 12s

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