Fixes for --out-path and --no-sysroot

This is a followup to [1].

Adds the build dir to the include path so the compiler can find
last_commit_position.h when the build dir is not "out".

Adds the necessary libs back on Linux when using --no-sysroot.

[1] https://gn.googlesource.com/gn/+/0e4f3935ee53741240a69b877a6a9aed78f62950

BUG=chromium:863460
R=brettw

Change-Id: Id76e88245d7b0a2489205700964d657e63acb59e
Reviewed-on: https://gn-review.googlesource.com/2180
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>

build/gen.py

diff --git a/build/gen.py b/build/gen.py
index fd0fa48..9dda914 100755
--- a/build/gen.py
+++ b/build/gen.py
@@ -249,7 +249,7 @@
   cflags_cc = os.environ.get('CXXFLAGS', '').split()
   ldflags = os.environ.get('LDFLAGS', '').split()
   libflags = os.environ.get('LIBFLAGS', '').split()
-  include_dirs = [REPO_ROOT]
+  include_dirs = [REPO_ROOT, os.path.dirname(path)]
   libs = []
 
   if is_posix:
@@ -269,16 +269,16 @@
     ])
     cflags_cc.extend(['-std=c++14', '-Wno-c++11-narrowing'])
 
-    if linux_sysroot:
-      # Use the sid sysroot that UpdateLinuxSysroot() downloads. We need to
-      # force the used of libstdc++ for now because libc++ is not in that
-      # sysroot and we don't currently have a local build of that. We should
-      # probably resolve this and (re-)add a way to build against libc++.
-      cflags.extend(['--sysroot=' + linux_sysroot,
-                     '-stdlib=libstdc++',
-                    ])
-      ldflags.extend(['--sysroot=' + linux_sysroot,
-                      '-static-libstdc++',
+    if is_linux:
+      if linux_sysroot:
+        # Use the sid sysroot that UpdateLinuxSysroot() downloads. We need to
+        # force the used of libstdc++ for now because libc++ is not in that
+        # sysroot and we don't currently have a local build of that. We should
+        # probably resolve this and (re-)add a way to build against libc++.
+        cflags.append('--sysroot=' + linux_sysroot)
+        ldflags.append('--sysroot=' + linux_sysroot)
+      cflags.append('-stdlib=libstdc++')
+      ldflags.extend(['-static-libstdc++',
                       '-stdlib=libstdc++',
                       '-Wl,--as-needed',
                      ])

tools/gn/gn_main.cc

diff --git a/tools/gn/gn_main.cc b/tools/gn/gn_main.cc
index b18c211..a61a752 100644
--- a/tools/gn/gn_main.cc
+++ b/tools/gn/gn_main.cc
@@ -16,7 +16,7 @@
 #include "util/msg_loop.h"
 #include "util/sys_info.h"
 
-#include "out/last_commit_position.h"
+#include "last_commit_position.h"
 
 namespace {