getgrnam, getgrgid, getpwnam, getpwuid for host

The functions now read /etc/group and /etc/passwd on host machines.
Android-specific IDs are not recognized in the host.

getpwent and getgrent are still not working though. They require a
bigger refactoring to sequentially advance in the database files.

Bug: 171718702
Test: run assemble_cvd in aosp_cf_arm64_phone
Change-Id: Ie8da382a467bbd0bffac7b4b8592cd871db80181
diff --git a/libc/bionic/grp_pwd_file.cpp b/libc/bionic/grp_pwd_file.cpp
index 81cf893..1f45e80 100644
--- a/libc/bionic/grp_pwd_file.cpp
+++ b/libc/bionic/grp_pwd_file.cpp
@@ -268,6 +268,7 @@
 
   while (line_beginning < end) {
     line_beginning = ParseLine(line_beginning, end, line->fields, line->kNumFields);
+#if defined(__ANDROID__)
     // To comply with Treble, users/groups from each partition need to be prefixed with
     // the partition name.
     if (required_prefix_ != nullptr) {
@@ -280,6 +281,7 @@
         continue;
       }
     }
+#endif
     if (predicate(line)) return true;
   }