versioner: refactor to use CompilerInstance directly.

This will make it easier to switch over to a virtual filesystem,
which should drastically improve performance.

This also fixes an issue with warning/error reporting.

Bug: http://b/32748936
Test: python run_tests.py
Change-Id: I2e967acf75db29c95f3a03f4f94cccd22c367ad5
diff --git a/libc/include/sys/ucontext.h b/libc/include/sys/ucontext.h
index fdb3015..4eddf23 100644
--- a/libc/include/sys/ucontext.h
+++ b/libc/include/sys/ucontext.h
@@ -29,8 +29,9 @@
 #ifndef _SYS_UCONTEXT_H_
 #define _SYS_UCONTEXT_H_
 
-#include <signal.h>
 #include <sys/cdefs.h>
+
+#include <signal.h>
 #include <sys/user.h>
 
 __BEGIN_DECLS