[RISCV] Define RISC-V specific e_flags
[RISCV] Define RISC-V specific e_flags

Add RISC-V e_flags as defined in the ABI document:

https://github.com/riscv/riscv-elf-psabi-doc/blob/master/riscv-elf.md#file-header

Differential Revision: https://reviews.llvm.org/D38310
Patch by Chih-Mao Chen.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@314386 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm