[Mips] Set default executable entry symbol name for MIPS targets. On MIPS the entry symbol name is '__start' instead of '_start'.
[Mips] Set default executable entry symbol name for MIPS targets. On
MIPS the entry symbol name is '__start' instead of '_start'.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@199235 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld