Move safe_strerror to posix directory and the base namespace.

Since this is a wrapper around a posix thing that doesn't fall under any other categories, the posix directory is probably the best place.

Review URL: https://codereview.chromium.org/1160373004

Cr-Original-Commit-Position: refs/heads/master@{#333524}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 6ee6fd6efabf8b87324d0b233ea2332c4a0e1642

tools/gn/bootstrap/bootstrap.py

diff --git a/tools/gn/bootstrap/bootstrap.py b/tools/gn/bootstrap/bootstrap.py
index 373883f..e2b35bc 100755
--- a/tools/gn/bootstrap/bootstrap.py
+++ b/tools/gn/bootstrap/bootstrap.py
@@ -247,11 +247,11 @@
         'base/files/file_util_posix.cc',
         'base/message_loop/message_pump_libevent.cc',
         'base/posix/file_descriptor_shuffle.cc',
+        'base/posix/safe_strerror.cc',
         'base/process/kill_posix.cc',
         'base/process/process_handle_posix.cc',
         'base/process/process_metrics_posix.cc',
         'base/process/process_posix.cc',
-        'base/safe_strerror_posix.cc',
         'base/synchronization/condition_variable_posix.cc',
         'base/synchronization/lock_impl_posix.cc',
         'base/synchronization/waitable_event_posix.cc',