Enable libnativehelper with linux_bionic

Making libnativehelper work with linux_bionic required giving
JNIHelp.cpp a more robust way of dealing with the differences between
glibc strerror_r and bionic/posix strerror_r.

Test: build
Test: run linux_bionic gtests
Bug: 31559095
Change-Id: I840f8c912f8a70c2afdaf7a1f2083e7b1f33c546