ARM: improve documentation slightly.

It seems the ARMv8 instruction set overview is no longer provided by ARM, so
I've removed it. Since most of the other documents were the same I unified the
two sections.

llvm-svn: 260329

Author: TNorthover

llvm/docs/CompilerWriterInfo.rst

@@ -13,25 +13,18 @@ Architecture & Platform Information for Compiler Writers
 Hardware
 ========
 
-ARM
----
+AArch64 & ARM
+-------------
 
-* `ARM documentation <http://www.arm.com/documentation/>`_ (`Processor Cores <http://www.arm.com/documentation/ARMProcessor_Cores/>`_ Cores)
+* `ARMv8-A Architecture Reference Manual <http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0487a.h/index.html>`_ (authentication required, free sign-up). This document covers both AArch64 and ARM instructions
 
-* `ABI <http://www.arm.com/products/DevTools/ABI.html>`_
+* `ARMv7-M Architecture Reference Manual` <http://infocenter.arm.com/help/topic/com.arm.doc.ddi0403e.b/index.html>`_ (authentication required, free sign-up). This covers the Thumb2-only microcontrollers
 
-* `ABI Addenda and Errata <http://infocenter.arm.com/help/topic/com.arm.doc.ihi0045d/IHI0045D_ABI_addenda.pdf>`_
+* `ARMv6-M Architecture Reference Manual` <http://infocenter.arm.com/help/topic/com.arm.doc.ddi0419c/index.html>_ (authentication required, free sign-up). This covers the Thumb1-only microcontrollers
 
 * `ARM C Language Extensions <http://infocenter.arm.com/help/topic/com.arm.doc.ihi0053c/IHI0053C_acle_2_0.pdf>`_
 
-AArch64
--------
-
-* `ARMv8 Architecture Reference Manual <http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0487a.h/index.html>`_
-
-* `ARMv8 Instruction Set Overview <http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.genc010197a/index.html>`_
-
-* `ARM C Language Extensions <http://infocenter.arm.com/help/topic/com.arm.doc.ihi0053c/IHI0053C_acle_2_0.pdf>`_
+* AArch32 `ABI Addenda and Errata <http://infocenter.arm.com/help/topic/com.arm.doc.ihi0045d/IHI0045D_ABI_addenda.pdf>`_
 
 Itanium (ia64)
 --------------