match glibc/lsb cancellation abi on i386

glibc made the ridiculous choice to use pass-by-register calling
convention for these functions, which is impossible to duplicate
directly on non-gcc compilers. instead, we use ugly asm to wrap and
convert the calling convention. presumably this works with every
compiler anyone could potentially want to use.

src/thread/i386/cancellation2.s

@@ -0,0 +1,16 @@
+.text
+.global __pthread_register_cancel
+.type   __pthread_register_cancel,%function
+__pthread_register_cancel:
+	pushl %eax
+	call __pthread_register_cancel_3
+	popl %eax
+	ret
+
+.global __pthread_unregister_cancel
+.type   __pthread_unregister_cancel,%function
+__pthread_unregister_cancel:
+	pushl %eax
+	call __pthread_unregister_cancel_3
+	popl %eax
+	ret

src/thread/i386/cancellation3.s

@@ -0,0 +1,8 @@
+.text
+.global __pthread_unwind_next
+.type   __pthread_unwind_next,%function
+__pthread_unwind_next:
+	pushl %eax
+	call __pthread_unwind_next_3
+	popl %eax
+	ret