Add posix_strerror_r.cpp to libbase

android_compile_dbg try build bot is failing with linker error.
```
ld.lld: error: undefined symbol: posix_strerror_r
>>> referenced by strings.cpp
```
Add posix_strerror_r.cpp which contains definition for symbol.

Bug: 1140633
Change-Id: Icdf5b6b513d9dc68a13e0bac53513ff75c574e61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/third_party/libunwindstack/+/3904551
Reviewed-by: Mike Wittman <wittman@chromium.org>
3 files changed