Use standard separator for TSan options in stress.cpp test case.

Use of space as a separator for options is problematic for wrapper
scripts (i.e. implementations of `%run`) that have to marshall
environment variables to target different than the host.

Rather than requiring every implementation of `%run` to support spaces
in `TSAN_OPTIONS` it is simpler to fix this single test case.

rdar://83637067

Differential Revision: https://reviews.llvm.org/D110967

compiler-rt/test/tsan/stress.cpp

@@ -1,4 +1,4 @@
-// RUN: %clangxx_tsan -O1 %s -o %t && %env_tsan_opts="flush_memory_ms=1 flush_symbolizer_ms=1 memory_limit_mb=1" %run %t 2>&1 | FileCheck %s
+// RUN: %clangxx_tsan -O1 %s -o %t && %env_tsan_opts=flush_memory_ms=1:flush_symbolizer_ms=1:memory_limit_mb=1 %run %t 2>&1 | FileCheck %s
 #include "test.h"
 #include <fcntl.h>
 #include <string.h>