Disable sysroot option when clang build is disabled

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 845ab5a1dc0e57e095f8a20bf10c1043755b2221..caa16b64c2043473f149110e48372eed443633d2 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -36,6 +36,12 @@
             # Use a raw surface abstraction.
             'use_ozone%': 0,
 
+            # By default we build against a stable sysroot image to avoid
+            # depending on the packages installed on the local machine. Set this
+            # to 0 to build against locally installed headers and libraries (e.g.
+            # if packaging for a linux distro)
+            'use_sysroot%': 1,
+
             # Configure the build for small devices. See crbug.com/318413
             'embedded%': 0,
 
@@ -57,6 +63,7 @@
           'use_ozone%': '<(use_ozone)',
           'embedded%': '<(embedded)',
           'host_arch%': '<(host_arch)',
+          'use_sysroot%': '<(use_sysroot)',
 
           # Whether we are using Views Toolkit
           'toolkit_views%': 0,
@@ -88,11 +95,11 @@
           # Enable Wayland display server support.
           'enable_wayland_server%' : 0,
 
-          # By default we build against a stable sysroot image to avoid
-          # depending on the packages installed on the local machine. Set this
-          # to 0 to build against locally installed headers and libraries (e.g.
-          # if packaging for a linux distro)
-          'use_sysroot%': 1,
+          # Set this to true when building with Clang.
+          # See http://code.google.com/p/chromium/wiki/Clang for details.
+          # If this is set, clang is used as both host and target compiler in
+          # cross-compile builds.
+          'clang%': 0,
 
           # Override buildtype to select the desired build flavor.
           # Dev - everyday build for development/testing
@@ -114,6 +121,15 @@
               'use_aura%': 1,
             }],
 
+            # Turn off use_sysroot when clang build is disabled.
+            # System headers for gcc > 4.6 aren't available at sysroot location.
+            # If clang build is disabled and gcc > 4.6, ToT builds fail.
+            # https://code.google.com/p/chromium/issues/detail?id=504446#c17
+            # TODO(kphanee): Can we check for gcc_version here somehow?
+            ['use_sysroot==1 and clang==0', {
+              'use_sysroot%': 0,
+            }],
+
             ['chromecast==1', {
               'use_libpci': 0,
               'conditions': [
@@ -171,6 +187,7 @@
         'branding_path_component%': '<(branding)',
         'host_arch%': '<(host_arch)',
         'target_arch%': '<(target_arch)',
+        'clang%': '<(clang)',
 
         'target_subarch%': '',
 
@@ -355,6 +372,7 @@
       'branding%': '<(branding)',
       'branding_path_component%': '<(branding_path_component)',
       'arm_version%': '<(arm_version)',
+      'clang%': '<(clang)',
       'sysroot%': '<(sysroot)',
       'chroot_cmd%': '<(chroot_cmd)',
       'system_libdir%': '<(system_libdir)',
@@ -625,11 +643,6 @@
 
       # Clang stuff.
       'make_clang_dir%': 'third_party/llvm-build/Release+Asserts',
-      # Set this to true when building with Clang.
-      # See http://code.google.com/p/chromium/wiki/Clang for details.
-      # If this is set, clang is used as both host and target compiler in
-      # cross-compile builds.
-      'clang%': 0,
 
       # Use experimental lld linker instead of the platform's default linker.
       'use_lld%': 0,