[bpf] add big- and host- endian support

Summary:
-march=bpf    -> host endian
-march=bpf_le -> little endian
-match=bpf_be -> big endian

Test Plan:
v1 was tested by IBM s390 guys and appears to be working there.
It bit rots too fast here.

Reviewers: chandlerc, tstellarAMD

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D10177

llvm-svn: 239071
diff --git a/llvm/test/CodeGen/BPF/ex1.ll b/llvm/test/CodeGen/BPF/ex1.ll
index be038e9..abf068c 100644
--- a/llvm/test/CodeGen/BPF/ex1.ll
+++ b/llvm/test/CodeGen/BPF/ex1.ll
@@ -1,4 +1,4 @@
-; RUN: llc < %s -march=bpf | FileCheck %s
+; RUN: llc < %s -march=bpf_le | FileCheck %s
 
 %struct.bpf_context = type { i64, i64, i64, i64, i64, i64, i64 }
 %struct.sk_buff = type { i64, i64, i64, i64, i64, i64, i64 }