make -emit-inline-file always write a file

[alicemaz]

presently, -emit-inline-file will not emit a file, and will delete one if it exists, if there are no exported procedures that can be inlined. this means in a pattern where you always emit for every -unit, and always consult for every -uses, compilation will halt if a file isn't found

it's a matter of opinion what the right thing to do here is, but I'm inclined to think a file should always be emitted if the flag is passed, even it's empty, because:

• it's consistent with how -emit-types-file behaves
• usage of the flag indicates user intent to create the file
• "absence of evidence isn't evidence of absence"--the existence of an empty file is an affirmative statement there is nothing to inline

note the deletion/omission behavor was added on purpose in 2010, so this isn't accidental, but I'm not sure the reasoning

tested on platform=LINUX

[megane]

Closed by 5df4ce1939c7450dfa481172204b6c898505e7a5