Improve handling of `InlineAsm` in `DefaultASTVisitor` #7993

Job	Run time
build-and-check-asan	30m 59s
build-and-check-clang-macos	40m 22s
build-and-check-gcc-48	29m 5s
build-and-check-ubuntu-64bit	26m 20s
build-and-check-ubuntu-32bit	25m 2s
build-and-check-ubuntu-64bit-glibcxx	28m 29s
	3h 0m 17s

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