[libc++] Don't alias quick_exit if __ANDROID_API__ < 21

Summary:
quick_exit() and at_quick_exit() were introduced in android NDK 21:
https://android.googlesource.com/platform/prebuilts/ndk/+/dev/platform/sysroot/usr/include/stdlib.h#55

This CL conditions `_LIBCPP_HAS_QUICK_EXIT` on `__ANDROID_API__ >= 21`.  The only place this macro is used is in some using declarations: `using ::quick_exit`, `using ::at_quick_exit`.

Also, add a missing include to sys/cdefs.h which is what defines `__BIONIC__`.

Reviewers: thakis, danalbert, EricWF

Reviewed By: danalbert

Subscribers: srhines, krytarowski

Differential Revision: https://reviews.llvm.org/D39479

llvm-svn: 317124

diff --git a/libcxx/include/__config b/libcxx/include/__config
index d621723..33cb9c4 100644 (file)
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -296,6 +296,10 @@
 #define _LIBCPP_NO_CFI
 #endif
 
+#if __libcpp_has_include(<sys/cdefs.h>)
+#include <sys/cdefs.h>
+#endif
+
 #if defined(_LIBCPP_COMPILER_CLANG)
 
 // _LIBCPP_ALTERNATE_STRING_LAYOUT is an old name for
@@ -407,7 +411,7 @@ typedef __char32_t char32_t;
 #define _LIBCPP_HAS_C11_FEATURES
 #elif defined(__linux__)
 #if !defined(_LIBCPP_HAS_MUSL_LIBC)
-#if __GLIBC_PREREQ(2, 15) || defined(__BIONIC__)
+#if __GLIBC_PREREQ(2, 15) || (defined(__BIONIC__) && (__ANDROID_API__ >= 21))
 #define _LIBCPP_HAS_QUICK_EXIT
 #endif
 #if __GLIBC_PREREQ(2, 17)