Remove i686-hosted Linux build and start switching to new directory layout

pnacl/README

 This file describes the directory layout of the PNaCl toolchain.
 
 The most important thing is the user-facing toolchain programs, including
 pnacl-clang, pnacl-clang++, pnacl-translate, etc. These are located in
 the bin/ directory. The location (and existence) of everything else is subject
 to change.
 
 bin/
-  User-facing toolchain programs (pnacl-clang, pnacl-translate, etc).
-  Currently these are OS-specific wrapper scripts.
-host_x86_32/
-  Executable toolchain binaries for x86-32 hosts. These are not intended to be
-  run directly; use the wrapper scripts in bin/
-host_x86_32/
-  Executable toolchain binaries for x86-64 hosts. These are not intended to be
-  run directly; use the wrapper scripts in bin/
-lib-arm/
-  Native NaCl object files and/or libraries linked into ARM nexes after
+  User-facing PNaCl toolchain programs (pnacl-clang, pnacl-translate, etc;
+  currently these are OS-specific wrapper scripts).
+  Standard LLVM tools such as llvm-nm, opt etc**
+  Nonstandard LLVM tools such as pnacl-llc**
+  Standard GNU binutils ELF tools
+include/
+  Headers for linking against our build of LLVM**
+lib/
+  Host libraries used by our build of LLVM**
+le32-nacl/
+  Bitcode libraries and headers for building PNaCl modules
+translator/
+  Native NaCl object files and/or libraries linked into nexes after
   offline translation.
-lib-mips32/
-  Native NaCl object files and/or libraries linked into MIPS nexes after
-  offline translation.
-lib-x86-32/
-  Native NaCl object files and/or libraries linked into x86-32 nexes after
-  offline translation.
-lib-x86-64/
-  Native NaCl object files and/or libraries linked into x86-64 nexes after
-  offline translation.
-lib/
-  Bitcode object files and/or libraries linked into user-generated pexes
-sdk/
-  Libraries and headers provided by the NaCl SDK which are not packaged with
-  the toolchain itself
-usr/
-  Libraries and headers packaged with the toolchain (e.g. libc, libm, libstdc++)
-  Naclports also installs its libraries and headers here.
-tools-arm/
-  Native ARM binaries used for testing (e.g. the standalone NaCl loader)
-tools-x86/
-  Native x86 binaries used for testing (e.g. x86 version of the ARM validator)
+
+**These are not generally needed directly by developers of PNaCl modules
+ in Chrome, but may be useful for others, e.g. those who want to build tools
+ which target PNaCl as a platform