Needed for binutils on x86.

diff -u -r /home/fornwall/lib/android-ndk/platforms/android-21/arch-x86/usr/include/sys/user.h ./usr/include/sys/user.h
--- /home/fornwall/lib/android-ndk/platforms/android-21/arch-x86/usr/include/sys/user.h	2014-12-01 19:05:05.000000000 -0500
+++ ./usr/include/sys/user.h	2014-12-23 10:31:31.343768553 -0500
@@ -99,6 +99,12 @@
   int u_debugreg[8];
 };
 
+/* http://osxr.org/android/source/bionic/libc/kernel/arch-x86/asm/user_32.h#0089 */
+#define NBPG PAGE_SIZE
+#define UPAGES 1
+#define HOST_TEXT_START_ADDR (u.start_code)
+#define HOST_STACK_END_ADDR (u.start_stack + u.u_ssize * NBPG)
+
 #elif defined(__x86_64__)
 
 struct user_fpregs_struct {