build: Fix broken OIIO_NO_NEON definition (#3911)

Clean up the `#if` tests that disable Intel SIMD when not on Intel
architectures, which incorrectly disabled ARM NEON when on ARM.

Fixes #3909

Signed-off-by: Larry Gritz <[email protected]>

Author: lgritz

src/include/OpenImageIO/simd.h

@@ -95,6 +95,9 @@
 #  ifndef OIIO_NO_AVX2
 #    define OIIO_NO_AVX2 1
 #  endif
+#endif
+
+#if !(defined(_M_ARM64) || defined(__aarch64) || defined(__aarch64__)) || defined(__CUDA_ARCH__)
 #  ifndef OIIO_NO_NEON
 #    define OIIO_NO_NEON 1
 #  endif