[libc++] Fix build with gcc 4.8

gcc 4.8.4 (but not 5.4.0 or 7.3.0) has trouble initializing errc with {}, giving
the error in [1]. This CL switches to explicitly using errc(0), which gcc 4.8
accepts.

[1] https://bugs.chromium.org/p/chromium/issues/detail?id=973723

Differential Revision: https://reviews.llvm.org/D63296


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@363333 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed