all: switch to LLVM 16

This commit adds support for LLVM 16 and switches to it by default. That
means three LLVM versions are supported at the same time: LLVM 14, 15,
and 16.

This commit includes work by QuLogic:

  * Part of this work was based on a PR by QuLogic:
    https://github.com/tinygo-org/tinygo/pull/3649
    But I also had parts of this already implemented in an old branch I
    already made for LLVM 16.
  * QuLogic also provided a CGo fix here, which is also incorporated in
    this commit:
    https://github.com/tinygo-org/tinygo/pull/3869

The difference with the original PR by QuLogic is that this commit is
more complete:
  * It switches to LLVM 16 by default.
  * It updates some things to also make it work with a self-built LLVM.
  * It fixes the CGo bug in a slightly different way, and also fixes
    another one not included in the original PR.
  * It does not keep compiler tests passing on older LLVM versions. I
    have found this to be quite burdensome and therefore don't generally
    do this - the smoke tests should hopefully catch most regressions.

builder/cc1as.h

@@ -82,6 +82,7 @@ struct AssemblerInvocation {
   unsigned NoExecStack : 1;
   unsigned FatalWarnings : 1;
   unsigned NoWarn : 1;
+  unsigned NoTypeCheck : 1;
   unsigned IncrementalLinkerCompatible : 1;
   unsigned EmbedBitcode : 1;
 
@@ -97,7 +98,14 @@ struct AssemblerInvocation {
 
   /// Darwin target variant triple, the variant of the deployment target
   /// for which the code is being compiled.
-  llvm::Optional<llvm::Triple> DarwinTargetVariantTriple;
+  std::optional<llvm::Triple> DarwinTargetVariantTriple;
+
+  /// The version of the darwin target variant SDK which was used during the
+  /// compilation
+  llvm::VersionTuple DarwinTargetVariantSDKVersion;
+
+  /// The name of a file to use with \c .secure_log_unique directives.
+  std::string AsSecureLogFile;
   /// @}
 
 public:
@@ -114,6 +122,7 @@ public:
     NoExecStack = 0;
     FatalWarnings = 0;
     NoWarn = 0;
+    NoTypeCheck = 0;
     IncrementalLinkerCompatible = 0;
     Dwarf64 = 0;
     DwarfVersion = 0;