Allocate thread local buffers in __init_tls.

Thread local buffers were using pthread_setspecific for storage with
lazy initialization. pthread_setspecific shares TLS slots between the
linker and libc.so, so thread local buffers being initialized in a
different order between libc.so and the linker meant that bad things
would happen (manifesting as snprintf not working because the
locale was mangled)

Bug: http://b/20464031
Test: /data/nativetest64/bionic-unit-tests/bionic-unit-tests
      everything passes
Test: /data/nativetest/bionic-unit-tests/bionic-unit-tests
      thread_local tests are failing both before and after (KUSER_HELPERS?)
Test: /data/nativetest64/bionic-unit-tests-static/bionic-unit-tests-static
      no additional failures
Change-Id: I9f445a77c6e86979f3fa49c4a5feecf6ec2b0c3f
diff --git a/libc/bionic/mntent.cpp b/libc/bionic/mntent.cpp
index 994b84d..92284ce 100644
--- a/libc/bionic/mntent.cpp
+++ b/libc/bionic/mntent.cpp
@@ -29,15 +29,11 @@
 #include <mntent.h>
 #include <string.h>
 
-#include "private/ThreadLocalBuffer.h"
-
-static ThreadLocalBuffer<mntent> g_getmntent_mntent_tls_buffer;
-static ThreadLocalBuffer<char, BUFSIZ> g_getmntent_strings_tls_buffer;
+#include "bionic/pthread_internal.h"
 
 mntent* getmntent(FILE* fp) {
-  return getmntent_r(fp, g_getmntent_mntent_tls_buffer.get(),
-                     g_getmntent_strings_tls_buffer.get(),
-                     g_getmntent_strings_tls_buffer.size());
+  auto& tls = __get_bionic_tls();
+  return getmntent_r(fp, &tls.mntent_buf, tls.mntent_strings, sizeof(tls.mntent_strings));
 }
 
 mntent* getmntent_r(FILE* fp, struct mntent* e, char* buf, int buf_len) {