Rename __dso_handle_so.c to __dso_handle_so.h

Also chang libc/arch-arm/bionic/crtbegin_so.c to include it
as a header.

Change-Id: Ib91b0b8caf5c8b936425aa8a4fc1a229b2b27929
diff --git a/libc/arch-arm/bionic/crtbegin_so.c b/libc/arch-arm/bionic/crtbegin_so.c
index f382f63..cd0257a 100644
--- a/libc/arch-arm/bionic/crtbegin_so.c
+++ b/libc/arch-arm/bionic/crtbegin_so.c
@@ -53,6 +53,6 @@
 #ifdef CRT_LEGACY_WORKAROUND
 #include "__dso_handle.h"
 #else
-#include "__dso_handle_so.c"
+#include "__dso_handle_so.h"
 #include "atexit.h"
 #endif