feat: backtick raw/multi-line strings + QBE backend fixes

- Add backtick raw string literals (Go-style ): no escape processing, multi-line
- C backend: handle backtick strings in emitExpr
- Self-hosted lexer: lexScanBacktickString support
- QBE backend: handle backtick strings in data sections
- QBE: remove broken extern declarations (QBE resolves at link time)
- QBE: fix comparison result types (ceql → w, extend to l)
- QBE: fix SSA parameter name clash (_p_ prefix for params)
- QBE: const inlining via HirLower + QBE emitter
- QBE: proper type mapping for bool/char types
- hir_lower: collect dkConst declarations for const propagation

src/c_backend.nim

@@ -160,8 +160,11 @@ proc emitExpr(be: var CBackend, node: HirNode): string =
       else: return "false"
     of tkStringLiteral:
       var text = node.litToken.text
+      # Backtick raw string: strip backticks, escape content for C
+      if text.len >= 2 and text[0] == '`' and text[text.len-1] == '`':
+        text = "\"" & cEscape(text[1 ..< text.len-1]) & "\""
       # If text has no surrounding quotes, it's from constFoldConstDecl (already unescaped)
-      if text.len >= 2 and text[0] == '"' and text[text.len-1] == '"':
+      elif text.len >= 2 and text[0] == '"' and text[text.len-1] == '"':
         # Strip c8" c16" c32" prefixes — in C they are just regular string literals
         if text.startsWith("c32\""):
           text = "\"" & cEscape(text[4 ..< text.len-1]) & "\""

src/lexer.nim

@@ -277,6 +277,18 @@ proc scanString(lex: var Lexer, startLoc: SourceLocation, prefixLen: int): Token
     discard lex.advance()  # closing "
   result = lex.makeToken(tkStringLiteral, startLoc, startPos)
 
+proc scanBacktickString(lex: var Lexer, startLoc: SourceLocation): Token =
+  ## Scan a backtick-delimited raw string literal: content is literal,
+  ## no escape processing, newlines are preserved.
+  let startPos = lex.pos - 1  # include the opening backtick
+  while not lex.isAtEnd() and lex.peek() != '`':
+    discard lex.advance()
+  if lex.isAtEnd():
+    lex.emitError(startLoc, "unterminated backtick string literal")
+  else:
+    discard lex.advance()  # closing backtick
+  result = lex.makeToken(tkStringLiteral, startLoc, startPos)
+
 proc scanChar(lex: var Lexer, startLoc: SourceLocation, prefixLen: int): Token =
   let startPos = lex.pos - prefixLen
   if lex.peek() == '\'':
@@ -523,6 +535,11 @@ proc nextToken(lex: var Lexer): Token =
   if c == '"':
     return lex.scanString(startLoc, 0)
 
+  # Backtick-delimited raw string: `...`
+  if c == '`':
+    discard lex.advance()
+    return lex.scanBacktickString(startLoc)
+
   # Char prefixes: c8' c16' c32' — must come before ident check
   if c == 'c' and lex.peek(1) in {'8', '1', '3'}:
     let d = lex.peek(1)

src/token.nim

@@ -5,7 +5,7 @@ type
     ##Literals
     tkIntLiteral      # 42  0xFF  0b1010  0o77
     tkFloatLiteral    # 3.14  1.0e-9
-    tkStringLiteral   # "hello"  c8"hello"  c16"hello"  c32"hello"
+    tkStringLiteral   # "hello"  c8"hello"  c16"hello"  c32"hello"  `raw multi-line`
     tkCharLiteral     # 'A'  c8'A'  c16'A'  c32'A'
     tkBoolLiteral     # true  false