Rgal/update readmes (#1)

* Update README files for new monorepo and flat project structure

Moved all details of the Program Repository project to top level
README.md and reverted "llvm" one to the upstream version.

* Move pstore to top level .gitignore

.gitignore

@@ -0,0 +1,2 @@
+# pstore, which is tracked independently.
+pstore/

README.md

@@ -1,3 +1,55 @@
+# LLVM with Program Repository Support
+
+This git repository contains a copy of LLVM (forked from commit 7b5565418f4d6e113ba805dad40d471d23bca6f6) with work-in-progress modifications to output to a Program Repository.
+
+The changes are to add support for the program repository that was first shown at the [2016 US LLVM Developers’ meeting](https://llvm.org/devmtg/2016-11/) in the talk catchily titled “Demo of a repository for statically compiled programs”. You can relive the highs and lows by [watching it on YouTube](https://youtu.be/-pL94rqyQ6c). The early implementation demonstrated there has its [own Github repository](https://github.com/SNSystems/Toy-tools): in essence, this work re-implements the same thing in LLVM to give you the anticipated build-time improvements in a C++ compiler targeting Linux. Further documentation can be found on the [project wiki](https://github.com/SNSystems/llvm-project-prepo/wiki).
+
+## Building the Compiler
+
+The process to follow is similar to that for a conventional build of Clang+LLVM, but with an extra step to get the [pstore](https://github.com/SNSystems/pstore) back-end.
+
+1. Clone llvm-project-prepo (this repository):
+
+        $ git clone https://github.com/SNSystems/llvm-project-prepo.git
+
+1. Clone [pstore](https://github.com/SNSystems/pstore):
+
+        $ cd llvm-project-prepo
+        $ git clone https://github.com/SNSystems/pstore.git
+        $ cd -
+
+   Ultimately, we envisage supporting multiple database back-ends to fit different needs, but there’s currently a hard dependency on the pstore (“Program Store”) key/value store as a back-end.
+
+
+1. Build LLVM as [normal](https://llvm.org/docs/CMake.html) enabling the clang and pstore subprojects (e.g.):
+
+        $ cmake -G "Ninja" -DLLVM_ENABLE_PROJECTS="clang;pstore" -DLLVM_TARGETS_TO_BUILD=X86 -DLLVM_TOOL_CLANG_TOOLS_EXTRA_BUILD=OFF ../llvm
+        $ ninja
+
+## Using the Program Repository
+
+### Compiling
+The program-repository is implemented as a new object-file format (“repo”) in LLVM. To use it, you need to request it explicitly in the target triple:
+
+    $ clang -target x86_64-pc-linux-gnu-repo -c -o test.o test.c
+
+Note that this is the only triple that we’re currently supporting (i.e. targeting X86-64 Linux).
+
+Furthermore, the path to the program-repository database itself is set using an environment variable `REPOFILE`; it that variable is not set, it defaults to `./clang.db` (eventually, you’d expect to be able to specify this path with a command-line switch).
+
+The command-line above will write the object code for `test.c` to the program-repository and emit a “ticket file” `test.o`. This tiny file contains a key to the real data in the database.
+
+### Linking
+A program-repository aware linker is very much on the project’s [“TODO” list](wiki/Limitations#missing-features). Until that happens, there's a `repo2obj` tool in the project tree. This generates a traditional ELF file from a repository ticket file. Using it is simple:
+
+    $ clang -target x86_64-pc-linux-gnu-repo -c -o test.o test.c
+    $ repo2obj test.o -o test.o.elf
+
+The first step compiles the source file `test.c` to the repository, the second will produce a file `test.o.elf` which can be fed to a traditional ELF linker.
+
+    $ clang -o test test.o.elf
+    $ ./test
+
 # The LLVM Compiler Infrastructure
 
 This directory and its subdirectories contain source code for LLVM,

llvm/.gitignore

@@ -67,8 +67,6 @@ tools/llgo
 tools/polly
 # avrlit, which is tracked independently.
 tools/avrlit
-# pstore, which is tracked independently.
-tools/pstore
 # Sphinx build tree, if building in-source dir.
 docs/_build
 # VS2017 and VSCode config files.

llvm/README.txt

@@ -0,0 +1,18 @@
+The LLVM Compiler Infrastructure
+================================
+
+This directory and its subdirectories contain source code for LLVM,
+a toolkit for the construction of highly optimized compilers,
+optimizers, and runtime environments.
+
+LLVM is open source software. You may freely distribute it under the terms of
+the license agreement found in LICENSE.txt.
+
+Please see the documentation provided in docs/ for further
+assistance with LLVM, and in particular docs/GettingStarted.rst for getting
+started with LLVM and docs/README.txt for an overview of LLVM's
+documentation setup.
+
+If you are writing a package for LLVM, see docs/Packaging.rst for our
+suggestions.
+