Merge remote-tracking branch 'origin/master' into llvm11

The changes to install_files.h needed to put into src/libcxx.zig

README.md

@@ -22,6 +22,8 @@ Note that you can
 
 ### Stage 1: Build Zig from C++ Source Code
 
+This step must be repeated when you make changes to any of the C++ source code.
+
 #### Dependencies
 
 ##### POSIX
@@ -69,6 +71,41 @@ make install
 
 See https://github.com/ziglang/zig/wiki/Building-Zig-on-Windows
 
+### Stage 2: Build Self-Hosted Zig from Zig Source Code
+
+Now we use the stage1 binary:
+
+```
+zig build --prefix $(pwd)/stage2 -Denable-llvm
+```
+
+This produces `stage2/bin/zig` which can be used for testing and development.
+Once it is feature complete, it will be used to build stage 3 - the final compiler
+binary.
+
+### Stage 3: Rebuild Self-Hosted Zig Using the Self-Hosted Compiler
+
+*Note: Stage 2 compiler is not yet able to build Stage 3. Building Stage 3 is
+not yet supported.*
+
+Once the self-hosted compiler can build itself, this will be the actual
+compiler binary that we will install to the system. Until then, users should
+use stage 1.
+
+#### Debug / Development Build
+
+```
+stage2/bin/zig build
+```
+
+This produces `zig-cache/bin/zig`.
+
+#### Release / Install Build
+
+```
+stage2/bin/zig build install -Drelease
+```
+
 ## License
 
 The ultimate goal of the Zig project is to serve users. As a first-order