[build] Use sysroot for linux compilation with clang

This ports the configuration for using a sysroot from
chromium's common.gypi.

This is restricted to clang only.

BUG=chromium:474921, chromium:616032
LOG=y

Review-Url: https://codereview.chromium.org/2028623002
Cr-Commit-Position: refs/heads/master@{#36729}

DEPS

@@ -189,6 +189,18 @@ hooks = [
                 "-s", "v8/buildtools/linux64/gn.sha1",
     ],
   },
+  {
+    # Downloads the current stable linux sysroot to build/linux/ if needed.
+    # This sysroot updates at about the same rate that the chrome build deps
+    # change.
+    'name': 'sysroot',
+    'pattern': '.',
+    'action': [
+        'python',
+        'v8/build/linux/sysroot_scripts/install-sysroot.py',
+        '--running-as-hook',
+    ],
+  },
   {
     # Update the Windows toolchain if necessary.
     'name': 'win_toolchain',

gypfiles/standalone.gypi

@@ -63,21 +63,52 @@
               'host_arch%': 'ia32',
             }],
           ],
+
+          # 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,
         },
         'host_arch%': '<(host_arch)',
         'target_arch%': '<(host_arch)',
+        'use_sysroot%': '<(use_sysroot)',
         'base_dir%': '<!(cd <(DEPTH) && python -c "import os; print os.getcwd()")',
 
         # Instrument for code coverage and use coverage wrapper to exclude some
         # files. Uses gcov if clang=0 is set explicitly. Otherwise,
         # sanitizer_coverage must be set too.
         'coverage%': 0,
+
+        # Default sysroot if no sysroot can be provided.
+        'sysroot%': '',
+
+        'conditions': [
+          # The system root for linux builds.
+          ['OS=="linux" and use_sysroot==1', {
+            'conditions': [
+              ['target_arch=="arm"', {
+                'sysroot%': '<!(cd <(DEPTH) && pwd -P)/build/linux/debian_wheezy_arm-sysroot',
+              }],
+              ['target_arch=="x64"', {
+                'sysroot%': '<!(cd <(DEPTH) && pwd -P)/build/linux/debian_wheezy_amd64-sysroot',
+              }],
+              ['target_arch=="ia32"', {
+                'sysroot%': '<!(cd <(DEPTH) && pwd -P)/build/linux/debian_wheezy_i386-sysroot',
+              }],
+              ['target_arch=="mipsel"', {
+                'sysroot%': '<!(cd <(DEPTH) && pwd -P)/build/linux/debian_wheezy_mips-sysroot',
+              }],
+            ],
+          }], # OS=="linux" and use_sysroot==1
+        ],
       },
       'base_dir%': '<(base_dir)',
       'host_arch%': '<(host_arch)',
       'target_arch%': '<(target_arch)',
       'v8_target_arch%': '<(target_arch)',
       'coverage%': '<(coverage)',
+      'sysroot%': '<(sysroot)',
       'asan%': 0,
       'lsan%': 0,
       'msan%': 0,
@@ -161,6 +192,7 @@
     'test_isolation_mode%': '<(test_isolation_mode)',
     'fastbuild%': '<(fastbuild)',
     'coverage%': '<(coverage)',
+    'sysroot%': '<(sysroot)',
 
     # Add a simple extras solely for the purpose of the cctests
     'v8_extra_library_files': ['../test/cctest/test-extra.js'],
@@ -627,6 +659,18 @@
               '-B<(base_dir)/third_party/binutils/Linux_x64/Release/bin',
             ],
           }],
+          ['sysroot!="" and clang==1', {
+            'target_conditions': [
+              ['_toolset=="target"', {
+                'cflags': [
+                  '--sysroot=<(sysroot)',
+                ],
+                'ldflags': [
+                  '--sysroot=<(sysroot)',
+                  '<!(<(DEPTH)/build/linux/sysroot_ld_path.sh <(sysroot))',
+                ],
+              }]]
+          }],
         ],
       },
     }],