[libc++] Use the no_destroy attribute to avoid destroying debug DB statics

Summary:
Otherwise, we can run into problems when the program has static variables
that need to use the debug database during their deinitialization, if
the debug DB has already been deinitialized.

Reviewers: EricWF

Subscribers: christof, jkorous, dexonsmith, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D60830

llvm-svn: 358602
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 81875a67b0d1bd43cca96b5e321a4af06b9299cd
diff --git a/src/debug.cpp b/src/debug.cpp
index 93fa1a8..7fdf90c 100644
--- a/src/debug.cpp
+++ b/src/debug.cpp
@@ -42,7 +42,7 @@
 __libcpp_db*
 __get_db()
 {
-    static __libcpp_db db;
+    static _LIBCPP_NO_DESTROY __libcpp_db db;
     return &db;
 }
 
@@ -64,7 +64,7 @@
 mutex_type&
 mut()
 {
-    static mutex_type m;
+    static _LIBCPP_NO_DESTROY mutex_type m;
     return m;
 }
 #endif // !_LIBCPP_HAS_NO_THREADS