[X86,AsmPrinter] Set assembler dialect for module inline asm

`clang -c -masm=intel` compiling a source file with file scope basic asm
incorrectly uses the AT&T dialect.
```
% cat a.c
asm("mov rax, rax");
% clang a.c -c -masm=intel
<inline asm>:1:1: error: unknown use of instruction mnemonic without a size suffix
mov rax, rax
^
```

Fix this by setting the assembler dialect from the MCAsmInfo object.

Note: `clang -c -flto -masm=intel a.c` still fails because of
https://reviews.llvm.org/D82862 for #34830: it tried to support AT&T
syntax for clang-cl, but the forced AT&T syntax is not compatible with
intended Intel syntax.

Pull Request: #85367

Author: MaskRay

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -538,8 +538,10 @@ bool AsmPrinter::doInitialization(Module &M) {
   if (!M.getModuleInlineAsm().empty()) {
     OutStreamer->AddComment("Start of file scope inline assembly");
     OutStreamer->addBlankLine();
-    emitInlineAsm(M.getModuleInlineAsm() + "\n", *TM.getMCSubtargetInfo(),
-                  TM.Options.MCOptions);
+    emitInlineAsm(
+        M.getModuleInlineAsm() + "\n", *TM.getMCSubtargetInfo(),
+        TM.Options.MCOptions, nullptr,
+        InlineAsm::AsmDialect(TM.getMCAsmInfo()->getAssemblerDialect()));
     OutStreamer->AddComment("End of file scope inline assembly");
     OutStreamer->addBlankLine();
   }

llvm/test/CodeGen/X86/asm-dialect-module.ll

@@ -0,0 +1,10 @@
+;; Test that we respect the assembler dialect when parsing module-level inline asm.
+; RUN: not llc < %s -mtriple=x86_64 2>&1 | FileCheck %s --check-prefix=ERR
+; RUN: llc < %s -mtriple=x86_64 -x86-asm-syntax=intel | FileCheck %s
+
+; ERR: <inline asm>:1:1: error: unknown use of instruction mnemonic without a size suffix
+
+; CHECK: .intel_syntax noprefix
+; CHECK: mov eax, eax
+
+module asm "mov eax, eax"