stage2: rework the C backend

 * std.ArrayList gains `moveToUnmanaged` and dead code
   `ArrayListUnmanaged.appendWrite` is deleted.
 * emit_h state is attached to Module rather than Compilation.
 * remove the implementation of emit-h because it did not properly
   integrate with incremental compilation. I will re-implement it
   in a follow-up commit.
 * Compilation: use the .codegen_failure tag rather than
   .dependency_failure tag for when `bin_file.updateDecl` fails.

C backend:
 * Use a CValue tagged union instead of strings for C values.
 * Cleanly separate state into Object and DeclGen:
   - Object is present only when generating a .c file
   - DeclGen is present for both generating a .c and .h
 * Move some functions into their respective Object/DeclGen namespace.
 * Forward decls are managed by the incremental compilation frontend; C
   backend no longer renders function signatures based on callsites.
   For simplicity, all functions always get forward decls.
 * Constants are managed by the incremental compilation frontend. C
   backend no longer has a "constants" section.
 * Participate in incremental compilation. Each Decl gets an ArrayList
   for its generated C code and it is updated when the Decl is updated.
   During flush(), all these are joined together in the output file.
 * The new CValue tagged union is used to clean up using of assigning to
   locals without an additional pointer local.
 * Fix bug with bitcast of non-pointers making the memcpy destination
   immutable.

1 files changed, 45 insertions, 0 deletions

diff --git a/src/link/C/zig.h b/src/link/C/zig.h
new file mode 100644
index 0000000000..49f97210eb
--- /dev/null
+++ b/src/link/C/zig.h
@@ -0,0 +1,45 @@
+#if __STDC_VERSION__ >= 199901L
+#include <stdbool.h>
+#else
+#define bool unsigned char
+#define true 1
+#define false 0
+#endif
+
+#if __STDC_VERSION__ >= 201112L
+#define zig_noreturn _Noreturn
+#elif __GNUC__
+#define zig_noreturn __attribute__ ((noreturn))
+#elif _MSC_VER
+#define zig_noreturn __declspec(noreturn)
+#else
+#define zig_noreturn
+#endif
+
+#if defined(__GNUC__)
+#define zig_unreachable() __builtin_unreachable()
+#else
+#define zig_unreachable()
+#endif
+
+#if defined(_MSC_VER)
+#define zig_breakpoint __debugbreak()
+#else
+#if defined(__MINGW32__) || defined(__MINGW64__)
+#define zig_breakpoint __debugbreak()
+#elif defined(__clang__)
+#define zig_breakpoint __builtin_debugtrap()
+#elif defined(__GNUC__)
+#define zig_breakpoint __builtin_trap()
+#elif defined(__i386__) || defined(__x86_64__)
+#define zig_breakpoint __asm__ volatile("int $0x03");
+#else
+#define zig_breakpoint raise(SIGTRAP)
+#endif
+#endif
+
+#include <stdint.h>
+#define int128_t __int128
+#define uint128_t unsigned __int128
+#include <string.h>
+