base: make boot_clock work on host linux, hide it on non-linux.

boot_clock was previously returning zero on any platform that doesn't
define __ANDROID__, including host bionic. Instead of returning a bogus
value, just hide it on non-Linux platforms.

Bug: http://b/37758947
Test: libbase_test32/64 on linux
Change-Id: I96e1d8b92dc44c6308408900cf0d27e1e7db5569
diff --git a/base/Android.bp b/base/Android.bp
index 81b96db..14bfe36 100644
--- a/base/Android.bp
+++ b/base/Android.bp
@@ -42,6 +42,7 @@
     clang: true,
     host_supported: true,
     srcs: [
+        "chrono_utils.cpp",
         "file.cpp",
         "logging.cpp",
         "parsenetaddress.cpp",
@@ -64,7 +65,6 @@
             srcs: [
                 "errors_unix.cpp",
                 "properties.cpp",
-                "chrono_utils.cpp",
             ],
             cppflags: ["-Wexit-time-destructors"],
             sanitize: {
@@ -74,14 +74,12 @@
         },
         darwin: {
             srcs: [
-                "chrono_utils.cpp",
                 "errors_unix.cpp",
             ],
             cppflags: ["-Wexit-time-destructors"],
         },
         linux_bionic: {
             srcs: [
-                "chrono_utils.cpp",
                 "errors_unix.cpp",
             ],
             cppflags: ["-Wexit-time-destructors"],
@@ -89,7 +87,6 @@
         },
         linux: {
             srcs: [
-                "chrono_utils.cpp",
                 "errors_unix.cpp",
             ],
             cppflags: ["-Wexit-time-destructors"],