[Clang][CFG] check children statements of asm goto

When performing CFG based analyses, don't forget to check the child
statements of an asm goto, such as the expressions used for
inputs+outputs.

Fixes: https://github.com/llvm/llvm-project/issues/51024
Fixes: https://github.com/ClangBuiltLinux/linux/issues/1439

Reviewed By: void, jyknight, jyu2, efriedma

Differential Revision: https://reviews.llvm.org/D116059