Add missing && to fix syntax.
#ifndef SANITIZER_PLATFORM_H
#define SANITIZER_PLATFORM_H
-#if !defined(__linux__) && !defined(__FreeBSD__) && !defined(__NetBSD__) \
+#if !defined(__linux__) && !defined(__FreeBSD__) && !defined(__NetBSD__) && \
!defined(__APPLE__) && !defined(_WIN32)
# error "This operating system is not supported"
#endif
