Update platform.h with correct Apple detection macro.
Imported from https://github.com/google/ruy/pull/334
PiperOrigin-RevId: 534429204
diff --git a/ruy/platform.h b/ruy/platform.h
index 825f873..f82ac11 100644
--- a/ruy/platform.h
+++ b/ruy/platform.h
@@ -108,7 +108,7 @@
// Enable on sufficiently recent Android NDK. Earlier versions had broken
// intrinsics headers.
#define RUY_PLATFORM_X86_ENHANCEMENTS 1
-#elif (defined(__APPLE_) || defined(__linux__)) && defined(__clang__) && \
+#elif (defined(__APPLE__) || defined(__linux__)) && defined(__clang__) && \
(__clang_major__ >= 8)
// Enable on recent versions of Clang. Might be possible
// to relax this version requirement.