[asan] disable MallocNanoZone for no fd test on darwin

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

Reviewed By: delcypher

Differential Revision: https://reviews.llvm.org/D98735

Author: aralisza

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

@@ -1,6 +1,11 @@
 // 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
 
@@ -10,9 +15,6 @@
 // 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>