Define xnn_float16 to be _Float16 if we detect that we are compiling … #3170

Job	Run time
build-and-test / cmake-linux-armhf	6m 57s
build-and-test / cmake-linux-riscv64	6m 15s
build-and-test / cmake-linux-riscv64-rvv	11m 47s
build-and-test / cmake-linux-aarch64	7m 5s
build-and-test / cmake-linux-x86_64	10m 3s
build-and-test / cmake-macos-arm64	10m 42s
build-and-test / cmake-windows-arm64	4m 26s
build-and-test / cmake-windows-x64	3m 51s
build-and-test / cmake-windows-x86	6m 12s
build-and-test / bazel-linux-aarch64	8m 26s
build-and-test / bazel-linux-x86_64-clang-18	11m 50s
build-and-test / cmake-android (arm64)	8m 7s
build-and-test / bazel-linux-x86_64-gcc-9	6m 52s
build-and-test / cmake-android (armv7)	7m 9s
build-and-test / cmake-ios-arm64	3m 37s
build-and-test / cmake-ios-x86_64	7m 3s
build-and-test / cmake-android (x86)	9m 37s
	2h 9m 59s

Provide feedback