[build] Use sysroot for linux compilation with clang

gypfiles/standalone.gypi

Index: gypfiles/standalone.gypi
diff --git a/gypfiles/standalone.gypi b/gypfiles/standalone.gypi
index d764e80b1f567561541e8356a82370f60271a943..ceda67136e4ec0220660cdd8808162586d273739 100644
--- a/gypfiles/standalone.gypi
+++ b/gypfiles/standalone.gypi
@@ -63,21 +63,51 @@
               '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,
+
+        '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',
+              }],
+            ],

[vogelheim, 2016/06/01 10:51:19]

I'm not sure what gyp does if OS is linux, use_sysroot is 1, but the target_arch
is different from those 4.

(Not sure this is worth fixing. The gyp conditional syntax is kind of horrible,
really.)

[Michael Achenbach, 2016/06/01 11:20:37]

I think it'll error out. So one should not set use_sysroot=1 in that case. An
if-else-if structure for the conditions above gets horribly nested in gyp. Or we
could provide a default on some structure level, but I think it's not worth it
as we can just set use_sysroot=0

+          }, {
+            '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,
@@ -165,6 +195,7 @@
     'fastbuild%': '<(fastbuild)',
     'coverage%': '<(coverage)',
     'has_valgrind%': '<(has_valgrind)',
+    'sysroot%': '<(sysroot)',
 
     # Add a simple extras solely for the purpose of the cctests
     'v8_extra_library_files': ['../test/cctest/test-extra.js'],
@@ -631,6 +662,18 @@
               '-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))',
+                ],
+              }]]
+          }],
         ],
       },
     }],