bionic: Implement getpwent and getgrent

Not efficient to iterate through given the large number of Android
ids (AID). Compile warning will result if you use these functions,
telling you as much. Not for general consumption, however for
example, some filesystem tests would like to see these to perform
all corners.

About 1/4 second for getpwent, and 1/8 second for getgrent to iterate
through all reserved Android aids.

Bug: 27999086
Change-Id: I7784273b7875c38e4954ae21d314f35e4bf8c2fc
diff --git a/libc/libc.arm.map b/libc/libc.arm.map
index 7a3b8bd..019a880 100644
--- a/libc/libc.arm.map
+++ b/libc/libc.arm.map
@@ -1276,12 +1276,18 @@
     catclose;
     catgets;
     catopen;
+    endgrent;
+    endpwent;
     getdomainname;
+    getgrent;
+    getpwent;
     getsubopt;
     hasmntopt;
     pthread_getname_np;
     quotactl;
     setdomainname;
+    setgrent;
+    setpwent;
     sighold;
     sigignore;
     sigpause;
@@ -1480,7 +1486,6 @@
     dlmalloc_inspect_all; # arm x86 mips nobrillo
     dlmalloc_trim; # arm x86 mips nobrillo
     dlmalloc_usable_size; # arm x86 mips nobrillo
-    endpwent; # arm x86 mips nobrillo
     fdprintf; # arm x86 mips nobrillo
     free_malloc_leak_info;
     ftime; # arm x86 mips nobrillo