Add llvmInlineAsm node

Add llvmInlineAsm node

InlineAsm node does not support memory clobbers.

gcc/rust/ChangeLog:

	* ast/rust-ast-collector.cc (TokenCollector::visit): Make visitor
	unreachable.
	* ast/rust-ast-collector.h: Add visit for LlvmInlineAsmNode.
	* ast/rust-ast-visitor.cc (DefaultASTVisitor::visit): Add visit
	function for the default ast visitor.
	* ast/rust-ast-visitor.h: Add function prototype.
	* ast/rust-ast.cc (LlvmInlineAsm::accept_vis): Add accept_vis to
	LlvmInlineAsm node.
	* ast/rust-ast.h: Add LlvmInlineAsm node kind.
	* ast/rust-expr.h (class LlvmInlineAsm): Add LlvmInlineAsm node.
	* expand/rust-derive.h: Add visit function for LlvmInlineAsm node.
	* expand/rust-macro-builtins-asm.cc (MacroBuiltin::llvm_asm_handler):
	Add handler for llvm inline assembly nodes.
	(parse_llvm_asm): Add function to parse llvm assembly nodes.
	* expand/rust-macro-builtins-asm.h (parse_llvm_asm): Add function
	prototypes.
	* expand/rust-macro-builtins.cc (inline_llvm_asm_maker): Add macro
	transcriber.
	* expand/rust-macro-builtins.h: Add transcriber function prototype.
	* hir/rust-ast-lower-base.cc (ASTLoweringBase::visit): Add visit
	function for LlvmInlineAsm node.
	* hir/rust-ast-lower-base.h: Add visit function prototype.
	* resolve/rust-ast-resolve-base.cc (ResolverBase::visit): Add visit
	function for LlvmInlineAsm node.
	* resolve/rust-ast-resolve-base.h: Add visit function prototype.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>