android: Use _FILE_OFFSET_BITS after all (undo dc3d480305b2)

The combination of _FILE_OFFSET_BITS=64 and unified headers with API <
21 hiding mmap() was a bug with the unified headers. It should be fixed
before NDK r15 is final. See https://crbug.com/711786.

Bug: crashpad:30
Change-Id: I744398899ab99df7afc489ad2e95911624c5e78a
Reviewed-on: https://chromium-review.googlesource.com/478992
Reviewed-by: Joshua Peraza <jperaza@chromium.org>

build/common.gypi

diff --git a/build/common.gypi b/build/common.gypi
index 610c670..8b68260 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -140,6 +140,9 @@
           '-fvisibility-inlines-hidden',
           '-std=c++11',
         ],
+        'defines': [
+          '_FILE_OFFSET_BITS=64',
+        ],
         'ldflags': [
           '-fPIC',
           '-pthread',
@@ -177,10 +180,6 @@
                 ],
               }],
             ],
-          }, {  # else: OS!="android"
-            'defines': [
-              '_FILE_OFFSET_BITS=64',
-            ],
           }],
         ],