[asan] disable MallocNanoZone for no fd test on darwin

[aralisza]

Summary

On Darwin, MallocNanoZone may log after execv, which messes up this test.
Disable MallocNanoZone for this test since we don't use it anyway with asan.

This environment variable should only affect Darwin and not change behavior on other platforms.

rdar://74992832

[aralisza]

comment`

[aralisza]

better comment

[aralisza]

fullstop

[aralisza]

actually include change this time

[delcypher]

LGTM

compiler-rt/test/asan/TestCases/Posix/no-fd.cpp

 // RUN: %clangxx_asan -std=c++11 -O0 %s -o %t
-// RUN: %run %t 2>&1 | FileCheck %s
-// RUN: %env_asan_opts=debug=1,verbosity=2 %run %t 2>&1 | FileCheck %s
+
+// MallocNanoZone=0 disables initialization of the Nano MallocZone on Darwin.
+// Initialization of this zone can interfere with this test because the zone
+// might log which opens another file descriptor,
+// e.g. failing to setup the zone due to ASan taking the memory region it wants.
+// RUN: env MallocNanoZone=0 %run %t 2>&1 | FileCheck %s
+// RUN: env MallocNanoZone=0 %env_asan_opts=debug=1,verbosity=2 %run %t 2>&1 | FileCheck %s
 
 // Test ASan initialization
 
 // This test closes the 0, 1, and 2 file descriptors before an exec() and relies
 // on them remaining closed across an execve(). This is not the case on newer
 // versions of Android. On PPC with ASLR turned on, this fails when linked with
 // lld - see https://bugs.llvm.org/show_bug.cgi?id=45076.
 // UNSUPPORTED: android, powerpc
 
-// Deflake this test before reinabling for darwin (rdar://74992832)
-// UNSUPPORTED: darwin
-
 #include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 
 extern "C" const char *__asan_default_options() {
   return "test_only_emulate_no_memorymap=1";
 }