Allow static C++ destructors to be properly called on dlclose().

With this patch, _and_ an upcoming build/ patch, the destruction
of static C++ objects contained in shared libraries will happen
properly when dlclose() is called.

Note that this change introduces crtbegin_so.S and crtend_so.S which
are currently ignored by the build system.

+ move definition of __dso_handle to the right place
  (before that, all shared libraries used the __dso_handle
   global variable from the C library).

  Note that we keep a 'weak' __dso_handle in aeabi.c to avoid
  breaking the build until the next patch to build/core/combo/
  appears. We will be able to remove that later.

+ move bionic/aeabi.c to arch-arm/bionic/ (its proper location)

Change-Id: Ie771aa204e3acbdf02fd30ebd4150373a1398f39
NOTE: The NDK will need to be modified to enable this feature in
      the shared libraries that are generated through it.
diff --git a/libc/arch-x86/bionic/crtbegin_dynamic.S b/libc/arch-x86/bionic/crtbegin_dynamic.S
index 3b47b18..88e7e6a 100644
--- a/libc/arch-x86/bionic/crtbegin_dynamic.S
+++ b/libc/arch-x86/bionic/crtbegin_dynamic.S
@@ -30,7 +30,7 @@
 	.globl _start
 
 # this is the small startup code that is first run when
-# any executable that is statically-linked with Bionic
+# any executable that is dynamically-linked with Bionic
 # runs.
 #
 # it's purpose is to call __libc_init with appropriate
@@ -94,3 +94,4 @@
 __CTOR_LIST__:
 	.long -1
 
+#include "__dso_handle.S"