Fix the check for Apple platforms. Mea culpa.

Change-Id: I48f5974b2650b0cdb07cfef8015b6ece6b8c2111
Reviewed-on: https://code-review.googlesource.com/c/re2/+/51981
Reviewed-by: Paul Wankadia <junyer@google.com>
diff --git a/re2/re2.h b/re2/re2.h
index 9bd1d13..956aeb1 100644
--- a/re2/re2.h
+++ b/re2/re2.h
@@ -196,7 +196,7 @@
 #include <mutex>
 #include <string>
 
-#ifdef __APPLE__
+#if defined(__APPLE__)
 #include <TargetConditionals.h>
 #endif
 
@@ -959,7 +959,7 @@
 // of Apple platforms that aren't macOS. If an iOS application really needs
 // the context pointee someday, we can get more specific then...
 #define RE2_HAVE_THREAD_LOCAL
-#if defined(__APPLE__) && defined(TARGET_OS_MAC) && !defined(TARGET_OS_OSX)
+#if defined(__APPLE__) && !TARGET_OS_OSX
 #undef RE2_HAVE_THREAD_LOCAL
 #endif