Actually disable RandTest.Fork on iOS.

TARGET_OS_IPHONE isn't defined without including <TargetConditionals.h>. Oops.
Confirmed now that OPENSSL_IOS gets defined where we expect.

Update-Note: There is some chance this will fail to build on some macOS host
builds of Android? https://codereview.chromium.org/538563002 suggests something
weird happens. However those Android builds of BoringSSL would already be
problematic because they'd set OPENSSL_STATIC_ARMCAP thinking they were iOS.
Thus I've intentionally kept the assumption that __APPLE__ implies a Darwin
target. If it goes through, all is well. If not, we'll learn more about that
configuration and that we likely need to revise our OPENSSL_APPLE definition.

Bug: chromium:890115
Change-Id: I1df73ac2321391d2449edbeb9cfa295fd607f935
Reviewed-on: https://boringssl-review.googlesource.com/32204
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/base.h b/include/openssl/base.h
index c0d7a8c..10f6e41 100644
--- a/include/openssl/base.h
+++ b/include/openssl/base.h
@@ -65,6 +65,10 @@
 #include <stdio.h>
 #endif
 
+#if defined(__APPLE__)
+#include <TargetConditionals.h>
+#endif
+
 // Include a BoringSSL-only header so consumers including this header without
 // setting up include paths do not accidentally pick up the system
 // opensslconf.h.