delete all stage1 c++ code not directly related to compiling stage2

Deleted 16,000+ lines of c++ code, including:
 * an implementation of blake hashing
 * the cache hash system
 * compiler.cpp
 * all the linking code, and everything having to do with building
   glibc, musl, and mingw-w64
 * much of the stage1 compiler internals got slimmed down since it
   now assumes it is always outputting an object file.

More stuff:
 * stage1 is now built with a different strategy: we have a tiny
   zig0.cpp which is a slimmed down version of what stage1 main.cpp used
   to be. Its only purpose is to build stage2 zig code into an object
   file, which is then linked by the host build system (cmake) into
   stage1. zig0.cpp uses the same C API that stage2 now has access to,
   so that stage2 zig code can call into stage1 c++ code.
   - stage1.h is
   - stage2.h is
   - stage1.zig is the main entry point for the Zig/C++
     hybrid compiler. It has the functions exported from Zig, called
     in C++, and bindings for the functions exported from C++, called
     from Zig.
 * removed the memory profiling instrumentation from stage1.
   Abandon ship!
 * Re-added the sections to the README about how to build stage2 and
   stage3.
 * stage2 now knows as a comptime boolean whether it is being compiled
   as part of stage1 or as stage2.
   - TODO use this flag to call into stage1 for compiling zig code.
 * introduce -fdll-export-fns and -fno-dll-export-fns and clarify
   its relationship to link_mode (static/dynamic)
 * implement depending on LLVM to detect native target cpu features when
   LLVM extensions are enabled and zig lacks CPU feature detection for
   that target architecture.
 * C importing is broken, will need some stage2 support to function
   again.

1 files changed, 2 insertions, 0 deletions

diff --git a/build.zig b/build.zig
index 17ee040e8f..9e5f2425c2 100644
--- a/build.zig
+++ b/build.zig
@@ -145,6 +145,7 @@ pub fn build(b: *Builder) !void {
     exe.addBuildOption([]const []const u8, "log_scopes", log_scopes);
     exe.addBuildOption([]const []const u8, "zir_dumps", zir_dumps);
     exe.addBuildOption(bool, "enable_tracy", tracy != null);
+    exe.addBuildOption(bool, "is_stage1", false);
     if (tracy) |tracy_path| {
         const client_cpp = fs.path.join(
             b.allocator,
@@ -165,6 +166,7 @@ pub fn build(b: *Builder) !void {
     const is_wasmtime_enabled = b.option(bool, "enable-wasmtime", "Use Wasmtime to enable and run WASI libstd tests") orelse false;
     const glibc_multi_dir = b.option([]const u8, "enable-foreign-glibc", "Provide directory with glibc installations to run cross compiled tests that link glibc");
 
+    test_stage2.addBuildOption(bool, "is_stage1", false);
     test_stage2.addBuildOption(bool, "have_llvm", enable_llvm);
     test_stage2.addBuildOption(bool, "enable_qemu", is_qemu_enabled);
     test_stage2.addBuildOption(bool, "enable_wine", is_wine_enabled);