Refactor OS_LINUX preprocessor directive for LaCrOS effort.

Currently, ChromeOS defines the OS_LINUX directive as well as
OS_CHROMEOS.  We're working to separate these two, so we're
making the fact that OS_LINUX == OS_LINUX || OS_CHROMEOS
explicit.

This is changes for /third_party/tcmalloc

This CL was uploaded by git cl split.

R=wfh@chromium.org

Bug: 1110266
Change-Id: I81296204a0e3914e22cb8fbfa3c07688c6fb63a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2370734
Reviewed-by: Will Harris <wfh@chromium.org>
Commit-Queue: Will Harris <wfh@chromium.org>
Auto-Submit: Sean McAllister <smcallis@google.com>
Cr-Commit-Position: refs/heads/master@{#801063}
GitOrigin-RevId: 48de5ae15ddb32cc5aa5b4bf143135002c06e2b6
diff --git a/src/system-alloc.cc b/src/system-alloc.cc
index 345e668..0dc8ab7 100644
--- a/src/system-alloc.cc
+++ b/src/system-alloc.cc
@@ -109,7 +109,7 @@
 
 namespace {
 
-#if defined(OS_LINUX) && defined(__x86_64__)
+#if (defined(OS_LINUX) || defined(OS_CHROMEOS)) && defined(__x86_64__)
 #define ASLR_IS_SUPPORTED
 #endif