[libunwind][mips] Modify the __mips_fpr macro check

The __mips_fpr macro can take the value of 0 as well, change to account for that case.

Differential Revision: https://reviews.llvm.org/D50245


git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@339848 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed