Ensure __set_errno is still visible on LP32.

The use of the .hidden directive to avoid going via the PLT for
__set_errno had the side-effect of actually making __set_errno
hidden (which is odd because assembler directives don't usually
affect symbols defined in a different file --- you can't even
create a weak reference to a symbol that's defined in a different
file).

This change switches the system call stubs over to a new always-hidden
__set_errno_internal and has a visible __set_errno on LP32 just for
binary compatibility with old NDK apps.

Bug: 17423135
Change-Id: I6b6d7a05dda85f923d22e5ffd169a91e23499b7b
diff --git a/libc/arch-mips/bionic/__bionic_clone.S b/libc/arch-mips/bionic/__bionic_clone.S
index 4b4498d..b216efe 100644
--- a/libc/arch-mips/bionic/__bionic_clone.S
+++ b/libc/arch-mips/bionic/__bionic_clone.S
@@ -66,7 +66,7 @@
 
 .L__error_bc:
 	move	a0,v0
-	la	t9,__set_errno
+	la	t9,__set_errno_internal
 	j	t9
 END(__bionic_clone)
 .hidden __bionic_clone
diff --git a/libc/arch-mips/bionic/syscall.S b/libc/arch-mips/bionic/syscall.S
index db477a5..5fed0ac 100644
--- a/libc/arch-mips/bionic/syscall.S
+++ b/libc/arch-mips/bionic/syscall.S
@@ -54,7 +54,7 @@
     j       ra
     nop
 1:
-    la      t9,__set_errno
+    la      t9,__set_errno_internal
     j       t9
     nop
     .set reorder
diff --git a/libc/arch-mips/bionic/vfork.S b/libc/arch-mips/bionic/vfork.S
index 96de69e..1849624 100644
--- a/libc/arch-mips/bionic/vfork.S
+++ b/libc/arch-mips/bionic/vfork.S
@@ -52,7 +52,7 @@
 	j	ra
 	 nop
 1:
-	la	t9, __set_errno
+	la	t9, __set_errno_internal
 	j	t9
 	 nop
 END(vfork)