Use ErrnoNumberAsString from libbase

Calling strerror_r is tricky, as glibc provides the GNU version
if _GNU_SOURCE is set, and musl libc only provides the posix version.
Handle the complexity once in libbase and reuse it here.

Bug: 190084016
Test: m USE_HOST_MUSL=true host-native
Change-Id: Id7b600d0cdd5804c75612c4d253637a281d3f0ff
diff --git a/common/utils.cc b/common/utils.cc
index 002e6a0..aa6c6b3 100644
--- a/common/utils.cc
+++ b/common/utils.cc
@@ -38,6 +38,7 @@
 #include <utility>
 #include <vector>
 
+#include <android-base/strings.h>
 #include <base/callback.h>
 #include <base/files/file_path.h>
 #include <base/files/file_util.h>
@@ -489,12 +490,6 @@
   return partition_name;
 }
 
-string ErrnoNumberAsString(int err) {
-  char buf[100];
-  buf[0] = '\0';
-  return strerror_r(err, buf, sizeof(buf));
-}
-
 bool FileExists(const char* path) {
   struct stat stbuf;
   return 0 == lstat(path, &stbuf);