all: fix LLVM version compatibility for targets and interp

cc1as: change AssemblerInvocation.Triple from std::string to
llvm::Triple, matching upstream LLVM 22 and fixing deprecation warnings
for lookupTarget, createMCRegInfo, createMCAsmInfo, and
createMCSubtargetInfo.

interp: always use ConstNamedStruct in rawValue.toLLVMValue instead of
falling back to ConstStruct for unnamed structs. LLVM 22 uses anonymous
identified struct types where previous versions used literal structs;
ConstStruct creates a literal type that doesn't match, causing an
"initializer type mismatch" panic for globals like fmt.ppFree.

compileopts: add build-tag-guarded feature patching for pre-LLVM 20
(strip +bulk-memory-opt and +call-indirect-overlong from wasm features)
and restructure into three files covering all LLVM version ranges.

targets: strip redundant negative features from RISC-V target JSONs
(esp32c3, esp32c6, fe310, k210, riscv-qemu, tkey). These ~190 negative
features per target listed every extension LLVM knows about that the
target doesn't use, but LLVM disables them by default. They became stale
across LLVM versions, causing "not a recognized feature" warnings. Keep
only positive features and -relax.

Signed-off-by: deadprogram <ron@hybridgroup.com>

builder/cc1as.h

@@ -20,7 +20,7 @@ struct AssemblerInvocation {
   /// @{
 
   /// The name of the target triple to assemble for.
-  std::string Triple;
+  llvm::Triple Triple;
 
   /// If given, the name of the target CPU to determine which instructions
   /// are legal.
@@ -142,7 +142,7 @@ struct AssemblerInvocation {
 
 public:
   AssemblerInvocation() {
-    Triple = "";
+    Triple = llvm::Triple();
     NoInitialTextSection = 0;
     InputFile = "-";
     OutputPath = "-";