LOCAL: use GNU-specific strerror_r() only if __GLIBC__ is not defined

This makes musl happy.
musl always chooses POSIX strerror_r().

str_error(3) suggests to use this condition:

(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600) && ! _GNU_SOURCE

but it doesn't work with musl. The only way to check is if __GLIBC__
is defined.

Change-Id: I30b508be65bfabd78cdbd73f63bcb222435cbcd5

asio/include/asio/impl/error_code.ipp

diff --git a/asio/include/asio/impl/error_code.ipp b/asio/include/asio/impl/error_code.ipp
index b996773..24e7ed8 100644
--- a/asio/include/asio/impl/error_code.ipp
+++ b/asio/include/asio/impl/error_code.ipp
@@ -101,7 +101,7 @@
 #elif defined(__MACH__) && defined(__APPLE__) \
   || defined(__NetBSD__) || defined(__FreeBSD__) || defined(__OpenBSD__) \
   || defined(_AIX) || defined(__hpux) || defined(__osf__) \
-  || defined(__ANDROID__)
+  || defined(__ANDROID__) || !defined(__GLIBC__)
     char buf[256] = "";
     using namespace std;
     strerror_r(value, buf, sizeof(buf));