linux: improve support for cross-compiling

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index cd48bb9641009f11f9e613b92bb4be107ecd7f40..3d6f1ea5970db40a81e3916739d8df47db77177a 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -101,6 +101,9 @@
 
     'chromeos%': 0,
 
+    # The system root for cross-compiles. Default: none.
+    'sysroot%': '',
+
     # This is the location of the sandbox binary. Chrome looks for this before
     # running the zygote process. If found, and SUID, it will be used to
     # sandbox the zygote process and, thus, all renderer processes.
@@ -532,6 +535,14 @@
               }],
             ],
           }],
+          ['sysroot!=""', {
+            'cflags': [
+              '--sysroot=<(sysroot)',
+            ],
+            'ldflags': [
+              '--sysroot=<(sysroot)',
+            ],
+          }],
           ['no_strict_aliasing==1', {
             'cflags': [
               '-fno-strict-aliasing',
@@ -766,4 +777,4 @@
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
-}
+}