Absolute pathnames should be avoided in #include directives because they make the program very nonportable.
Somehow, the quote above sounds weird.
Can we use "very" with an adjective that starts with "non"?
Is "very non-adjective" grammatical?
Yes, it is perfectly grammatical to apply very to an adjective beginning with non-.
However, that says nothing about whether it is sensible, which varies according to the word. It’s easier to be very nonchalant than very nonpareil.
Some are glad to admit modifiers of degree like very, really, or highly, while others do so only in extended, figurative senses. And some seem completely unfriendly to the idea.
All this is true no matter whether the prefix is non-, un-, or in-/im-/ir-/il-.
Note that most of these can — and quite often, should — be spelled without the hyphen, as in nonblack for non-black.
Additionally, applying negations like not or hardly to such words may not be uncumbersome outside of certain device of rhetoric (read: litotes).
The reason it sounds weird to you is because an adjective like "nonconforming" or "nonspecific" reflects a state or condition which is absolute and complete, and does not allow for any degrees of intensity. When we say "non" something, we are aware of describing a binary state: the thing either is or isn't something, and if it isn't, it isn't. It seems on the face of it as if we can't say "very" because the thing can't be more (or less) of not being the something in question.
Think of a light switch. When it is in the "off" position, and the light is off (which we can think of as "non-on"), it's is simply the case that the light isn't on. It can't be more non-on; it can't be more off than off, so "very off" doesn't make literal sense.
On the other hand, we do have a tendency to use the language in particular ways for particular purposes, no matter what any rule might say. We are capable of saying, "very non-something," whether it is sensible or not, and whether it is grammatical or not. But the fact is that English allows it; it is not ungrammatial. So even though on the face of it it make seem to be lacking sense, we often say something like "the light is very off," for the simple reason that we want to emphasize how dark it is.
Use of the term "very" with "non-" adjectives is generally problematic not because "non-" adjectives are not gradable, but rather because many of them are gradable in multiple independent ways and it would be unclear which of those ways "very" should modify. Generally, for the term "very" to be usable with an adjective, there must be some means be which things that differ may be ranked, and such usage is not possible with many non-adjectives.
For example, for an implementation to be deemed "compliant" it would have to meet a variety of specifications. An implementation which met eleven of twelve specifications and was close to meeting the twelfth would be "non-compliant", as would an implementation which wasn't even close to meeting any of them, but the degrees of non-conformity would differ. On the other hand, it's hardly clear whether an implementation which met eleven specifications perfectly and was nowhere near meeting the twelfth would be "more" or "less" non-compliant than one which was very close to meeting each specification, but didn't quite meet any of them. One could use "thoroughly non-compliant" to suggest that an implementation didn't come meaningfully close to meeting any of the relevant specifications, but "very" is simply too vague.
Another difficulty which arises is that in many cases when a "non-" adjective is used, it will be used to refer to things which have not been identified as having some trait; even if the trait would be gradable, the identification is not. For example, if one draws 100 marbles of various sizes from a bag, the number of "large" marbles and the number of "non-large" marbles must be equal to 100. By contrast, the number of "large" marbles and the number of "small" marbles might total to less than 100 if there were some marbles that were neither large nor small. Even though "large" would generally be a gradable adjective, its usage here is absolute, describing not the actual size of the marble, but how it was classified. If the "large" bag is supposed to contain all the marbles which weigh 20 grams or more, and nothing smaller than that, but because of imprecision in the weighing apparatus a 19g marble gets put in that bag and a 21g marble does not, the 19g marble would be "large" and the 21g marble "non-large".