Fix parsing of unsigned constants.

We were using strtol(3) so unsigned constants that wouldn't fit in a
signed int were not parsed correctly.

Fix by using strtoul(3) on signed overflow.

Bug: crbug.com/657508
Test: syscall_filter_unittest
Change-Id: I7a986cf6c5f3a84dbd8605861794e9d7ef9c4ce7
3 files changed