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 /build

This CL was uploaded by git cl split.

R=tikuta@chromium.org

Bug: 1110266
Change-Id: Id461b5872c27e7a3f7b4df922e44cc2e073f9dd1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2371212
Auto-Submit: Sean McAllister <smcallis@google.com>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800889}
GitOrigin-RevId: 863b1c2cf409b9929772de52e37d7e5ed3b460e2

build_config.h

@@ -104,9 +104,9 @@
 
 // For access to standard POSIXish features, use OS_POSIX instead of a
 // more specific macro.
-#if defined(OS_AIX) || defined(OS_ANDROID) || defined(OS_ASMJS) || \
-    defined(OS_CHROMEOS) || defined(OS_FREEBSD) || defined(OS_IOS) || \
-    defined(OS_LINUX) || defined(OS_MAC) || defined(OS_NACL) || \
+#if defined(OS_AIX) || defined(OS_ANDROID) || defined(OS_ASMJS) ||  \
+    defined(OS_FREEBSD) || defined(OS_IOS) || defined(OS_LINUX) ||  \
+    defined(OS_CHROMEOS) || defined(OS_MAC) || defined(OS_NACL) ||  \
     defined(OS_NETBSD) || defined(OS_OPENBSD) || defined(OS_QNX) || \
     defined(OS_SOLARIS)
 #define OS_POSIX 1