Name the thread stack and signal stack guard pages.

Bug: http://b/22228722
Change-Id: I1dae672e386e404fb304a34496a29fe21134c784
diff --git a/libc/bionic/pthread_create.cpp b/libc/bionic/pthread_create.cpp
index dbdb180..e260e97 100644
--- a/libc/bionic/pthread_create.cpp
+++ b/libc/bionic/pthread_create.cpp
@@ -87,6 +87,7 @@
     // We can only use const static allocated string for mapped region name, as Android kernel
     // uses the string pointer directly when dumping /proc/pid/maps.
     prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ss.ss_sp, ss.ss_size, "thread signal stack");
+    prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, stack_base, PAGE_SIZE, "thread signal stack guard page");
   }
 }
 
@@ -140,6 +141,7 @@
     munmap(space, mmap_size);
     return NULL;
   }
+  prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, space, stack_guard_size, "thread stack guard page");
 
   return space;
 }