Take a quick_exit() patch from upstream FreeBSD.

  r325389 | kib | 2017-11-04 03:52:58 -0700 (Sat, 04 Nov 2017) | 7 lines

  C++17 requires quick_exit(3) to be async-signal safe.

  Make it safe, and update man page with the useful information.

  Sponsored by: The FreeBSD Foundation
  MFC after:  1 week

Test: treehugger
Change-Id: Idf84b1f1e360c031b0e39d5f6e80d17308db1940
diff --git a/libc/upstream-freebsd/android/include/freebsd-compat.h b/libc/upstream-freebsd/android/include/freebsd-compat.h
index 6f7a3f0..3228701 100644
--- a/libc/upstream-freebsd/android/include/freebsd-compat.h
+++ b/libc/upstream-freebsd/android/include/freebsd-compat.h
@@ -47,4 +47,6 @@
 /* FreeBSD has this, but we can't really implement it correctly on Linux. */
 #define issetugid() 0
 
+#define __compiler_membar() __asm __volatile(" " : : : "memory")
+
 #endif
diff --git a/libc/upstream-freebsd/android/include/machine/atomic.h b/libc/upstream-freebsd/android/include/machine/atomic.h
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/libc/upstream-freebsd/android/include/machine/atomic.h