[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: https://github.com/llvm/llvm-project/pull/85367