Fix a bug introduced in r305092 on big-endian systems.

Summary:
We were writing the length of the string based on system-endianness, and
not universally little-endian.  This fixes that.

Reviewers: zturner

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D34159

llvm-svn: 305322