Revert "Revert "More pthreads cleanup.""

This reverts commit 6f94de3ca4

(Doesn't try to increase the number of TLS slots; that leads to
an inability to boot. Adds more tests.)

Change-Id: Ia7d25ba3995219ed6e686463dbba80c95cc831ca

libc/bionic/strerror_r.cpp

@@ -7,6 +7,8 @@
 #include <stdio.h>
 #include <string.h>
 
+#include "private/ErrnoRestorer.h"
+
 struct Pair {
   int code;
   const char* msg;
@@ -42,7 +44,7 @@ extern "C" __LIBC_HIDDEN__ const char* __strsignal_lookup(int signal_number) {
 }
 
 int strerror_r(int error_number, char* buf, size_t buf_len) {
-  int saved_errno = errno;
+  ErrnoRestorer errno_restorer;
   size_t length;
 
   const char* error_name = __strerror_lookup(error_number);
@@ -52,11 +54,10 @@ int strerror_r(int error_number, char* buf, size_t buf_len) {
     length = snprintf(buf, buf_len, "Unknown error %d", error_number);
   }
   if (length >= buf_len) {
-    errno = ERANGE;
+    errno_restorer.override(ERANGE);
     return -1;
   }
 
-  errno = saved_errno;
   return 0;
 }